scsi: megaraid_sas: add correct return type check for ldio hint logic for raid1

Return value check of atomic_dec_if_positive is required as it returns
old value minus one.  Without this fix, driver will send small ios to
firmware path and that will be a performance issue.

Not critical, but good to have r1_ldio_hint as default value in sdev
private.

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