btrfs: scrub: initialize ret in scrub_simple_mirror() to fix compilation warning

[ Upstream commit b4e585f ]

The following error message is displayed:
  ../fs/btrfs/scrub.c:2152:9: error: ‘ret’ may be used uninitialized
  in this function [-Werror=maybe-uninitialized]"

Compiler version: gcc version: (Debian 10.2.1-6) 10.2.1 20210110

Reviewed-by: Boris Burkov <[email protected]>
Signed-off-by: Lu Yao <[email protected]>
Reviewed-by: David Sterba <[email protected]>
Signed-off-by: David Sterba <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>

Author: Lu Yao

fs/btrfs/scrub.c

@@ -3407,7 +3407,7 @@ static int scrub_simple_mirror(struct scrub_ctx *sctx,
 	const u32 max_length = SZ_64K;
 	struct btrfs_path path = { 0 };
 	u64 cur_logical = logical_start;
-	int ret;
+	int ret = 0;
 
 	/* The range must be inside the bg */
 	ASSERT(logical_start >= bg->start && logical_end <= bg->start + bg->length);