swscale/slice: Actually use the buffers' strides

Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>

libswscale/slice.c

@@ -159,9 +159,9 @@ int ff_init_slice_from_src(SwsSlice * s, uint8_t *src[4], int stride[4], int src
                         lumY + lumH};
 
     const uint8_t *src_[4] = {src[0] + (relative ? 0 : start[0]) * stride[0],
-                              src[1] + (relative ? 0 : start[1]) * stride[0],
-                              src[2] + (relative ? 0 : start[2]) * stride[0],
-                              src[3] + (relative ? 0 : start[3]) * stride[0]};
+                              src[1] + (relative ? 0 : start[1]) * stride[1],
+                              src[2] + (relative ? 0 : start[2]) * stride[2],
+                              src[3] + (relative ? 0 : start[3]) * stride[3]};
 
     s->width = srcW;