scsi: megaraid_sas: Return the DCMD status from megasas_get_seq_num

In megasas_get_seq_num, the status of the DCMD fired to FW is not
returned, it always returns success.  We could end up registering AEN
request with incorrect sequence number if the DCMD failed.  Return the
DCMD status back to caller.  This was discovered during code review and
very rare to see issue in field to see AEN request failed bt FW.

Signed-off-by: Shivasharan S <shivasharan.srikanteshwara@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>