btrfs: assign error values to the correct bio structs

Fixes: 4246a0b63bd8 ("block: add a bi_error field to struct bio")
Signed-off-by: Junjie Mao <junjie.mao@enight.me>
Acked-by: David Sterba <dsterba@suse.cz>
Cc: stable@vger.kernel.org # 4.3+
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/btrfs/compression.c

@@ -698,7 +698,7 @@ int btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 
 			ret = btrfs_map_bio(root, comp_bio, mirror_num, 0);
 			if (ret) {
-				bio->bi_error = ret;
+				comp_bio->bi_error = ret;
 				bio_endio(comp_bio);
 			}
 
@@ -728,7 +728,7 @@ int btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 
 	ret = btrfs_map_bio(root, comp_bio, mirror_num, 0);
 	if (ret) {
-		bio->bi_error = ret;
+		comp_bio->bi_error = ret;
 		bio_endio(comp_bio);
 	}