fix condition

Author: RayeS2070

cmake/UserverGrpcTargets.cmake

@@ -67,7 +67,7 @@ function(_userver_prepare_grpc)
     if(NOT gRPC_VERSION)
         message(FATAL_ERROR "Invalid gRPC package")
     endif()
-    if(NOT PROTOBUF_PROTOC AND NOT $<TARGET_FILE:protobuf::protoc>)
+    if(NOT PROTOBUF_PROTOC AND NOT TARGET protobuf::protoc)
         message(FATAL_ERROR "protoc not found")
     endif()
     if(NOT PROTO_GRPC_CPP_PLUGIN)