scsi: zfcp: replace zfcp_qdio_sbale_count by sg_nents

The zfcp_qdio_sbale_count function do the same work than sg_nents().
So replace it by sg_nents() for removing duplicate code.

Signed-off-by: LABBE Corentin <clabbe.montjoie@gmail.com>
Signed-off-by: Steffen Maier <maier@linux.vnet.ibm.com>
Signed-off-by: Benjamin Block <bblock@linux.vnet.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>