mpt3sas: simplify ->change_queue_depth

Merge two functions, and remove overly verbose debugging output that pokes
into mid-layer internal structures.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Mike Christie <michaelc@cs.wisc.edu>
Reviewed-by: Hannes Reinecke <hare@suse.de>