xfs: widen flags argument to the xfs_iflags_* helpers

xfs_inode.i_flags is an unsigned long, so make these helpers take that
as the flags argument instead of unsigned short.  This is needed for the
next patch.

While we're at it, remove the iflags variable from xfs_iget_cache_miss
because we no longer need it.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Andrey Albershteyn <aalbersh@redhat.com>