xfs: require both realtime inodes to mount

xfs: require both realtime inodes to mount

[ Upstream commit 64bafd2f1e484e27071e7584642005d56516cb77 ]

Since mkfs always formats the filesystem with the realtime bitmap and
summary inodes immediately after the root directory, we should expect
that both of them are present and loadable, even if there isn't a
realtime volume attached.  There's no reason to skip this if rbmino ==
NULLFSINO; in fact, this causes an immediate crash if the there /is/ a
realtime volume and someone writes to it.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Bill O'Donnell <billodo@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>