fix bug of set cuda lib in demo_ci and infer_ut (#41811)

paddle/fluid/inference/api/demo_ci/CMakeLists.txt

@@ -85,7 +85,7 @@ if(WITH_GPU)
     set(CUDA_LIB "/usr/local/cuda/lib64/" CACHE STRING "CUDA Library")
   else()
     set(CUDA_LIB "" CACHE STRING "CUDA_LIB")
-    if("${TENSORRT_ROOT}" STREQUAL "")
+    if("${CUDA_LIB}" STREQUAL "")
       if(DEFINED ENV{CUDA_PATH})
         set(CUDA_LIB "$ENV{CUDA_PATH}\\lib\\x64")
       else()

paddle/fluid/inference/tests/infer_ut/CMakeLists.txt

@@ -84,7 +84,7 @@ if(WITH_GPU)
     set(CUDA_LIB "/usr/local/cuda/lib64/" CACHE STRING "CUDA Library")
   else()
     set(CUDA_LIB "" CACHE STRING "CUDA_LIB")
-    if("${TENSORRT_ROOT}" STREQUAL "")
+    if("${CUDA_LIB}" STREQUAL "")
       if(DEFINED ENV{CUDA_PATH})
         set(CUDA_LIB "$ENV{CUDA_PATH}\\lib\\x64")
       else()