Fix Cuda compilation (#317)

Author: wangwenxin0312

ucm/sparse/kvstar/retrieve/CMakeLists.txt

@@ -1,14 +1,8 @@
 # auto detect cuda ------------------------
 if($ENV{PLATFORM} STREQUAL "cuda")
     if(NOT DEFINED CMAKE_CUDA_COMPILER)
-        set(CUDA_HOME "$ENV{CUDA_HOME}")
-        if(NOT CUDA_HOME)
-            set(CUDA_HOME "/usr/local/cuda")
-        endif()
-        if(NOT EXISTS "${CUDA_HOME}")
-            message(FATAL_ERROR "CUDA_HOME directory does not exist: ${CUDA_HOME}")
-        endif()
-        set(CMAKE_CUDA_COMPILER "${CUDA_HOME}/bin/nvcc" CACHE FILEPATH "CUDA compiler" FORCE)
+        set(CUDA_ROOT "/usr/local/cuda/" CACHE PATH "Path to CUDA root directory")
+        set(CMAKE_CUDA_COMPILER ${CUDA_ROOT}/bin/nvcc)
     endif()
     enable_language(CUDA)
     set(CMAKE_CUDA_ARCHITECTURES 75 80 86 89 90)