ibmvscsi: use H_CLOSED instead of magic number

In a couple places the magic value of 2 is used to check the return code
of hypercalls. This translates to H_CLOSED.

Signed-off-by: Tyrel Datwyler <tyreld@linux.vnet.ibm.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>