ntfs: fix uninitialized variable in ntfs_write_simple_iomap_begin_non_resident

Smatch reported that err could be used uninitialized if the code path
does not enter the first ntfs_zero_range() block.

Reported-by: Dan Carpenter <error27@gmail.com>
Reviewed-by: Hyunchul Lee <hyc.lee@gmail.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>

Author: namjaejeon

fs/ntfs/iomap.c

@@ -384,7 +384,7 @@ static int ntfs_write_simple_iomap_begin_non_resident(struct inode *inode, loff_
 	loff_t vcn_ofs, rl_length;
 	struct runlist_element *rl, *rlc;
 	bool is_retry = false;
-	int err;
+	int err = 0;
 	s64 vcn, lcn;
 	s64 max_clu_count =
 		ntfs_bytes_to_cluster(vol, round_up(length, vol->cluster_size));