qla2xxx: Avoid using variable-length arrays

This patch does not change any functionality but avoids that sparse
complains about using variable-length arrays.

Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Acked-by: Himanshu Madhani <himanshu.madhani@cavium.com>
Cc: Quinn Tran <quinn.tran@cavium.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>