scsi: qla2xxx: Reduce the scope of three local variables in qla2xxx_queuecommand()

This patch makes it clear that the tag, hwq and qpair variables are only
used in the mq path.

Cc: Himanshu Madhani <hmadhani@marvell.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Tested-by: Himanshu Madhani <hmadhani@marvell.com>
Reviewed-by: Himanshu Madhani <hmadhani@marvell.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>