[SCSI] qla4xxx: fix queue depth setting

We want to set the queue depth to something reasonable - not
the can_queue.

Signed-off-by: Mike Christie <michaelc@cs.wisc.edu>
Cc: David Somayajulu <david.somayajulu@qlogic.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>