ext4: fix an IS_ERR() vs NULL check

The ext4_find_extent() function never returns NULL, it returns error
pointers.

Fixes: 44059e503b03 ("ext4: fast commit recovery path")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20201023112232.GB282278@mwandaSigned-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org

fs/ext4/extents.c

@@ -5815,8 +5815,8 @@ int ext4_ext_replay_update_ex(struct inode *inode, ext4_lblk_t start,
 	int ret;
 
 	path = ext4_find_extent(inode, start, NULL, 0);
-	if (!path)
-		return -EINVAL;
+	if (IS_ERR(path))
+		return PTR_ERR(path);
 	ex = path[path->p_depth].p_ext;
 	if (!ex) {
 		ret = -EFSCORRUPTED;