swscale/x86/swscale: Fix warning about loosing significant bits in cast

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libswscale/x86/swscale.c

@@ -201,7 +201,7 @@ static void yuv2yuvX_sse3(const int16_t *filter, int filterSize,
                            const int16_t **src, uint8_t *dest, int dstW,
                            const uint8_t *dither, int offset)
 {
-    if(((int)dest) & 15){
+    if(((uintptr_t)dest) & 15){
         yuv2yuvX_mmxext(filter, filterSize, src, dest, dstW, dither, offset);
         return;
     }