cmake: fix KLEIDICV_SOURCE_PATH handling

On 5.x branch, commit c3ca3f4f was accidentally reverted, so the
external KleidiCV will be silently disabled. Revert these changes to
support external KleidiCV builds.

Signed-off-by: Weizhao Ouyang <o451686892@gmail.com>

cmake/OpenCVFindLibsPerf.cmake

@@ -211,6 +211,7 @@ endif()
 # --- ARM KleidiCV
 if(WITH_KLEIDICV)
   if(KLEIDICV_SOURCE_PATH AND EXISTS "${KLEIDICV_SOURCE_PATH}/adapters/opencv/CMakeLists.txt")
+    message(STATUS "Use external KleidiCV ${KLEIDICV_SOURCE_PATH}")
     set(HAVE_KLEIDICV ON)
   endif()
   if(NOT HAVE_KLEIDICV)
@@ -219,8 +220,6 @@ if(WITH_KLEIDICV)
     if(KLEIDICV_SOURCE_PATH)
       set(HAVE_KLEIDICV ON)
     endif()
-  else()
-    set(HAVE_KLEIDICV OFF)
   endif()
 endif(WITH_KLEIDICV)