FPHSA: Fix empty version message in exact match

`find_package_check_version()` would use variable `_FOUND_VERSION` set
by `find_package_handle_standard_args()` in a single branch when doing
exact matching, causing empty version messages if it was instead called
directly.

This was missed in commit 6bfc442fde (FPHSA: add support of version
range, 2020-09-22, v3.19.0-rc1~122^2~1) when the version check was moved
into its own function.

Modules/FindPackageHandleStandardArgs.cmake

@@ -342,7 +342,7 @@ function(FIND_PACKAGE_CHECK_VERSION version result)
           set(version_msg "Found unsuitable version \"${version}\", but required is exact version \"${${package}_FIND_VERSION}\"")
         else ()
           set(version_ok TRUE)
-          set(version_msg "(found suitable exact version \"${_FOUND_VERSION}\")")
+          set(version_msg "(found suitable exact version \"${version}\")")
         endif ()
       else ()
         if (NOT ${package}_FIND_VERSION VERSION_EQUAL version)