scsi: aacraid: Improve code readability

aac_queuecommand() is a scsi_host_template.queuecommand()
implementation. Any value returned by this function other than one of
the following values is translated into SCSI_MLQUEUE_HOST_BUSY:

* 0
* SCSI_MLQUEUE_HOST_BUSY
* SCSI_MLQUEUE_DEVICE_BUSY
* SCSI_MLQUEUE_EH_RETRY
* SCSI_MLQUEUE_TARGET_BUSY

Improve readability of aac_queuecommand() by returning
SCSI_MLQUEUE_HOST_BUSY instead of FAILED.

Cc: Gilbert Wu <gilbert.wu@microchip.com>
Cc: Sagar Biradar <Sagar.Biradar@microchip.com>
Cc: John Garry <john.g.garry@oracle.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: John Garry <john.g.garry@oracle.com>
Link: https://patch.msgid.link/20251021201743.3539900-1-bvanassche@acm.org
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>