scsi: aacraid: Move code to wait for IO completion to shutdown func

Ideally driver needs to wait for IO to be submitted or responded to before
shutdown.

Move code to wait for IO completion into shutdown path

Signed-off-by: Raghava Aditya Renukunta <RaghavaAditya.Renukunta@microsemi.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>