scsi: megaraid_sas: Change max_cmd from u32 to u16 in all functions

Since maximum supported FW commands are all defined as u16, change
all local variables referring to max_cmd from u32 to u16.

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>