scsi: megaraid_sas: Use Block layer API to check SCSI device in-flight IO requests

Remove usage of device_busy counter from driver. Instead of device_busy
counter now driver uses 'nr_active' counter of request_queue to get the
number of inflight request for a LUN.

Link: https://lore.kernel.org/r/1579000882-20246-11-git-send-email-anand.lodnoor@broadcom.com
Link : https://patchwork.kernel.org/patch/11249297/


Signed-off-by: Chandrakanth Patil <chandrakanth.patil@broadcom.com>
Signed-off-by: Anand Lodnoor <anand.lodnoor@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>