phase2: fix stray closing parenthesis

Due to the stray closing parenthesis introduced in commit f0faed2
("phase2: compute checksums") we have currently we've failing checksum
step in phase2:

 argv: b'cd bin/packages/mipsel_24kc_24kf; find . -type f -not -name \'sha256sums\' -printf "%P\n" | sort | xargs -r ../../../staging_dir/host/bin/mkhash -n sha256 | sed -ne \'s!^\\(.*\\) \\(.*\\)$!\x01 *\x02!p\' > sha256sums)'
 environment:
  ...snip...
  using PTY: False
 /bin/sh: 2: Syntax error: ")" unexpected
 program finished with exit code 2

Fixes: f0faed2 ("phase2: compute checksums")
Reported-by: Hannu Nyman <[email protected]>
Signed-off-by: Petr Štetiar <[email protected]>

phase2/master.cfg

@@ -736,7 +736,7 @@ for arch in arches:
             command="cd bin/packages/%s; " % (arch[0])
             + "find . -type f -not -name 'sha256sums' -printf \"%P\n\" | "
             + "sort | xargs -r ../../../staging_dir/host/bin/mkhash -n sha256 | "
-            + "sed -ne 's!^\(.*\) \(.*\)$!\1 *\2!p' > sha256sums)",
+            + "sed -ne 's!^\(.*\) \(.*\)$!\1 *\2!p' > sha256sums",
             haltOnFailure=True,
         )
     )