[SCSI] fix up non-modular SCSI

The recent change to the way scsi_device_get()/put() work broke the
non modular build (we do a module_refcount on a NULL).  Fix this by
checking for non-null before checking module_refcount().

Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>
1 file changed