scsi: megaraid_sas: max_fw_cmds are decremented twice, remove duplicate

Fix to account for the reply_q_sz not exceeding the maximum commands
that the firmware can support, instance->max_fw_cmds is already
decremented in megasas_fusion_update_can_queue().  Remove the extra
decrement logic in code.

Signed-off-by: Kashyap Desai <kashyap.desai@broadcom.com>
Signed-off-by: Shivasharan S <shivasharan.srikanteshwara@broadcom.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Tomas Henzl <thenzl@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>