scsi: megaraid_sas: enable intx only if msix request fails

Without this fix, driver will enable INTx Interrupt pin even though
MSI-x vectors are enabled. See below lspci output. DisINTx is unset for
MSIx setup.

lspci -s 85:00.0 -vvv |grep INT |grep Control
Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr-
Stepping- SERR+ FastB2B- DisINTx-

After applying this fix, driver will enable INTx Interrupt pin only if
Legacy interrupt method is required.  See below lspci output. DisINTx is
set for MSIx setup.  lspci -s 85:00.0 -vvv |grep INT |grep Control
Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr-
Stepping- SERR+ FastB2B- DisINTx+

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