xfs: remove the NULL fork handling in xfs_bmapi_read

xfs: remove the NULL fork handling in xfs_bmapi_read

Source kernel commit: 4b516ff4e772993a99fc9bf36503d23ce5bd5ba9

Now that we fully verify the inode forks before they are added to the
inode cache, the crash reported in

https://bugzilla.kernel.org/show_bug.cgi?id=204031

can't happen anymore, as we'll never let an inode that has inconsistent
nextents counts vs the presence of an in-core attr fork leak into the
inactivate code path.  So remove the work around to try to handle the
case, and just return an error and warn if the fork is not present.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>