ext4: minor fix for ext4_split_extent_zeroout()

We missed storing the error which triggerd smatch warning:

	fs/ext4/extents.c:3369 ext4_split_extent_zeroout()
	warn: duplicate zero check 'err' (previous on line 3363)

fs/ext4/extents.c
    3361
    3362         err = ext4_ext_get_access(handle, inode, path + depth);
    3363         if (err)
    3364                 return err;
    3365
    3366         ext4_ext_mark_initialized(ex);
    3367
    3368         ext4_ext_dirty(handle, inode, path + depth);
--> 3369         if (err)
    3370                 return err;
    3371
    3372         return 0;
    3373 }

Fix it by correctly storing the err value from ext4_ext_dirty().

Link: https://lore.kernel.org/all/aYXvVgPnKltX79KE@stanley.mountain/
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Fixes: a985e07 ("ext4: refactor zeroout path and handle all cases")
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Signed-off-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Baokun Li <libaokun@linux.alibaba.com>
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Link: https://patch.msgid.link/20260302143811.605174-1-ojaswin@linux.ibm.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org

Author: OjaswinM

fs/ext4/extents.c

@@ -3363,7 +3363,7 @@ static int ext4_split_extent_zeroout(handle_t *handle, struct inode *inode,
 
 	ext4_ext_mark_initialized(ex);
 
-	ext4_ext_dirty(handle, inode, path + depth);
+	err = ext4_ext_dirty(handle, inode, path + depth);
 	if (err)
 		return err;