ntfs: capture mft mirror sync errors in ntfs_write_mft_block()

ntfs: capture mft mirror sync errors in ntfs_write_mft_block()

After ntfs_sync_mft_mirror() became able to return real I/O errors,
ntfs_write_mft_block() still discards its return value at the call
site inside the per-record loop.  A failed $MFTMirr write therefore
leaves the volume looking clean from the writeback path even though
the on-disk mirror is now stale.

Capture the return value and feed it into the function's existing
@err variable using the same "first error wins" pattern already used
on other failure paths.  The error is propagated to the caller and,
via the existing tail of the function, sets NVolErrors so umount and
chkdsk see the volume as inconsistent.

Fixes: 115380f9a2f9 ("ntfs: update mft operations")
Signed-off-by: DaeMyung Kang <charsyam@gmail.com>
Reviewed-by: Hyunchul Lee <hyc.lee@gmail.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>