FindCUDA/select_compute_arch: Restore two-component CUDA_VERSION

Since commit v3.12.0-rc1~332^2 (FindCUDA/select_compute_arch: Add
support for CUDA as a language, 2018-03-15) this module sets
`CUDA_VERSION` based on `CMAKE_CUDA_COMPILER_VERSION` when the language
is enabled.  Limit it to two components for consistency with the
normal `FindCUDA` documentation and behavior.

Fixes: #18231

Modules/FindCUDA/select_compute_arch.cmake

@@ -18,8 +18,9 @@
 #
 
 if(CMAKE_CUDA_COMPILER_LOADED) # CUDA as a language
-  if(CMAKE_CUDA_COMPILER_ID STREQUAL "NVIDIA")
-    set(CUDA_VERSION "${CMAKE_CUDA_COMPILER_VERSION}")
+  if(CMAKE_CUDA_COMPILER_ID STREQUAL "NVIDIA"
+      AND CMAKE_CUDA_COMPILER_VERSION MATCHES "^([0-9]+\\.[0-9]+)")
+    set(CUDA_VERSION "${CMAKE_MATCH_1}")
   endif()
 endif()