libobs: Restore casts to fix Clang warnings

Clang doesn't like it if you convert T** to const T* const* without
casting even though it should be safe. Might be a C language thing.

libobs/obs-source.c

@@ -1687,11 +1687,13 @@ bool update_async_texture(struct obs_source *source,
 		return false;
 
 	if (type == CONVERT_420)
-		decompress_420(frame->data, frame->linesize,
+		decompress_420((const uint8_t* const*)frame->data,
+				frame->linesize,
 				0, frame->height, ptr, linesize);
 
 	else if (type == CONVERT_NV12)
-		decompress_nv12(frame->data, frame->linesize,
+		decompress_nv12((const uint8_t* const*)frame->data,
+				frame->linesize,
 				0, frame->height, ptr, linesize);
 
 	else if (type == CONVERT_422_Y)