udf: Ignore [ug]id=ignore mount options

Currently uid=ignore and gid=ignore make no sense without uid=<number>
and gid=<number> respectively as they result in all files having invalid
uid / gid which then doesn't allow even root to modify files and thus
causes confusion. And since commit ca76d2d8 "UDF: fix UID and GID
mount option ignorance" (from over 10 years ago) uid=<number> overrides
all uids on disk as uid=ignore does. So just silently ignore uid=ignore
mount option.

Reviewed-by: Pali Rohár <pali.rohar@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>