[XFS] Fix build brakage from patch "Clean up dquot pincount code"

This is a fix for patch " Clean up dquot pincount code" which introduced a
build breakage due to a missing & in xfs_qm_dquot_logitem_pin.

SGI-PV: 986789

SGI-Modid: xfs-linux-melb:xfs-kern:32221a

Signed-off-by: Peter Leckie <pleckie@sgi.com>
Signed-off-by: Donald Douwsma <donaldd@sgi.com>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>