gfs2: fix timestamp handling on quota inodes

While these aren't generally visible from userland, it's best to be
consistent with timestamp handling. When adjusting the quota, update the
mtime and ctime like we would with a write operation on any other inode,
and avoid updating the atime which should only be done for reads.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Andreas Gruenbacher <agruenba@redhat.com>
Message-Id: <20230713135249.153796-1-jlayton@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>