[xnnpack] Update cmake help message

Author: digantdesai

backends/xnnpack/CMakeLists.txt

@@ -39,7 +39,7 @@ option(EXECUTORCH_XNNPACK_SHARED_WORKSPACE
 # Keeping this OFF by default due to regressions in decode
 # and model load with kleidi kernels
 option(EXECUTORCH_XNNPACK_ENABLE_KLEIDI
-  "Enable workspace sharing across different delegate instances" OFF)
+  "Enable Arm Kleidi kernels" OFF)
 if(EXECUTORCH_XNNPACK_SHARED_WORKSPACE)
   add_definitions(-DENABLE_XNNPACK_SHARED_WORKSPACE)
 endif()