scsi: megaraid_sas: Incorrect processing of IOCTL frames for SMP/STP commands

cmd->frame->dcmd.opcode will be valid only for MFI_CMD_DCMD
IOCTL frames. Currently driver check for cmd->frame->dcmd.opcode without
checking cmd type. Ensure we check dcmd opcode only for MFI_CMD_DCMD
commands. Separate handling of MFI_CMD_SMP/STP commands from
MFI_CMD_DCMD in completion path.

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