fix a deadlock

0  up_testset (lock=0x404241c0 <g_uart1priv+32>) at /home/hujun5/下载/vela_sim/nuttx/include/arch/spinlock.h:96
1  spin_lock_wo_note (lock=<optimized out>) at /home/hujun5/下载/vela_sim/nuttx/include/nuttx/spinlock.h:207
2  spin_lock_irqsave_wo_note (lock=0x404241c0 <g_uart1priv+32>) at /home/hujun5/下载/vela_sim/nuttx/include/nuttx/spinlock.h:467
3  spin_lock_irqsave (lock=0x404241c0 <g_uart1priv+32>) at /home/hujun5/下载/vela_sim/nuttx/include/nuttx/spinlock.h:521
4  pl011_txint (dev=0x404240b0 <g_uart1port>, enable=false) at serial/uart_pl011.c:746
5  0x00000000402a3f1c in uart_xmitchars (dev=0x404240b0 <g_uart1port>) at serial/serial_io.c:118
6  0x00000000402a10f8 in pl011_txint (dev=<optimized out>, enable=<optimized out>) at serial/uart_pl011.c:756
7  0x00000000402a2ca0 in uart_write (filep=<optimized out>, buffer=<optimized out>, buflen=0) at serial/serial.c:1493
8  0x000000004028c464 in file_writev_compat (filep=0x4046cda0, uio=<optimized out>) at vfs/fs_write.c:81
9  0x000000004028c588 in file_writev (filep=<optimized out>, uio=uio@entry=0x40470dc0) at vfs/fs_write.c:161
10 0x000000004028c5fc in nx_writev (fd=<optimized out>, iov=iov@entry=0x40470e10, iovcnt=iovcnt@entry=1) at vfs/fs_write.c:257
11 0x000000004028c660 in writev (fd=<optimized out>, iov=iov@entry=0x40470e10, iovcnt=iovcnt@entry=1) at vfs/fs_write.c:356
12 0x000000004028c6dc in write (fd=<optimized out>, buf=buf@entry=0x404090b2 <g_nshgreeting>, nbytes=<optimized out>) at vfs/fs_write.c:421
13 0x00000000402adb10 in nsh_session (pstate=pstate@entry=0x40471080, login=login@entry=1, argc=argc@entry=1, argv=argv@entry=0x4046cf40) at nsh_session.c:108
14 0x00000000402ad94c in nsh_consolemain (argc=argc@entry=1, argv=argv@entry=0x4046cf40) at nsh_consolemain.c:75
15 0x00000000402ad894 in nsh_main (argc=argc@entry=1, argv=argv@entry=0x4046cf40) at nsh_main.c:74
16 0x00000000402a5880 in nxtask_startup (entrypt=0x402ad7fc <nsh_main>, argc=1, argv=0x4046cf40) at sched/task_startup.c:72
17 0x000000004029d444 in nxtask_start () at task/task_start.c:116
18 0x0000000000000000 in ?? ()

fix regresion from #15301

Signed-off-by: hujun5 <[email protected]>

drivers/serial/uart_pl011.c

@@ -748,19 +748,15 @@ static void pl011_txint(FAR struct uart_dev_s *dev, bool enable)
   if (enable)
     {
       pl011_irq_tx_enable(sport);
-
-      /* Fake a TX interrupt here by just calling uart_xmitchars() with
-       * interrupts disabled (note this may recurse).
-       */
+      spin_unlock_irqrestore(&sport->lock, flags);
 
       uart_xmitchars(dev);
     }
   else
     {
       pl011_irq_tx_disable(sport);
+      spin_unlock_irqrestore(&sport->lock, flags);
     }
-
-  spin_unlock_irqrestore(&sport->lock, flags);
 }
 
 /***************************************************************************