scsi: aacraid: Fix potential null access

Currently, command threads fails to return ioctls commands for older
controller versions, since it returns when all the fibs have been
allocated. Another issue is even all the fibs have not been allocated,
the correct allocated fibs is not updated nor freed.

Fixes: 113156bc (scsi: aacraid: Reworked aac_command_thread)
Reported-by: Tomas Henzl <thenzl@redhat.com>
Signed-off-by: Raghava Aditya Renukunta <RaghavaAditya.Renukunta@microsemi.com>
Reviewed-by: Dave Carroll <david.carroll@microsemi.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>