cmake: fix setting CMAKE_HIP_FLAGS (#3155)

Fix
#2523 (comment).


[`CMAKE_<LANG>_FLAGS`](https://cmake.org/cmake/help/latest/variable/CMAKE_LANG_FLAGS.html#variable:CMAKE_%3CLANG%3E_FLAGS)
is a string, so when using `set`, we should use quotes.

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

source/lib/src/gpu/CMakeLists.txt

@@ -73,9 +73,10 @@ elseif(USE_ROCM_TOOLKIT)
 
   message(STATUS "HIP major version is " ${hip_VERSION_MAJOR})
 
-  set(CMAKE_HIP_FLAGS -fno-gpu-rdc ${CMAKE_HIP_FLAGS}) # --amdgpu-target=gfx906
+  set(CMAKE_HIP_FLAGS "-fno-gpu-rdc ${CMAKE_HIP_FLAGS}"
+  )# --amdgpu-target=gfx906
   if(hip_VERSION VERSION_LESS 3.5.1)
-    set(CMAKE_HIP_FLAGS -hc ${CMAKE_HIP_FLAGS})
+    set(CMAKE_HIP_FLAGS "-hc ${CMAKE_HIP_FLAGS}")
   endif()
 
   file(GLOB SOURCE_FILES "*.cu")