Use %% for inline assembly rather than % so this compiles with clang.

Same as https://github.com/opencv/opencv/pull/8525/commits/9210cefb36868e201f7e0c8b84e4ee4f91b5432b but for this file too.

modules/core/include/opencv2/core/cuda/warp.hpp

@@ -64,7 +64,7 @@ namespace cv { namespace cuda { namespace device
         static __device__ __forceinline__ unsigned int laneId()
         {
             unsigned int ret;
-            asm("mov.u32 %0, %laneid;" : "=r"(ret) );
+            asm("mov.u32 %0, %%laneid;" : "=r"(ret) );
             return ret;
         }