FindHDF5: Fix H5_VERSION on Patch in C

Fix a typo from commit v3.6.0-rc1~85^2 (HDF5: Refactor the use of
compiler wrappers, 2016-04-04) that accidentally used the HDF5 C++
version (which could be empty) while detecting the C patch version.
The detection failed for patch releases, such as `1.10.0-patch1`
becoming `.1` instead of `1.10.0.1`.

Modules/FindHDF5.cmake

@@ -214,7 +214,7 @@ function(_HDF5_test_regular_compiler_C success version is_parallel)
     )
     set(${version} ${CMAKE_MATCH_1})
     if(CMAKE_MATCH_3)
-      set(${version} ${HDF5_CXX_VERSION}.${CMAKE_MATCH_3})
+      set(${version} ${HDF5_C_VERSION}.${CMAKE_MATCH_3})
     endif()
     set(${version} ${${version}} PARENT_SCOPE)