yuv2rgb: fix integer overflow in fill_table

Fixes CID703748
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libswscale/yuv2rgb.c

@@ -667,7 +667,7 @@ SwsFunc ff_yuv2rgb_get_func_ptr(SwsContext *c)
 }
 
 static void fill_table(uint8_t* table[256 + 2*YUVRGB_TABLE_HEADROOM], const int elemsize,
-                       const int inc, void *y_tab)
+                       const int64_t inc, void *y_tab)
 {
     int i;
     uint8_t *y_table = y_tab;