mtip32xx: blk_mq_init_queue() returns an ERR_PTR

We changed this from blk_alloc_queue_node() to blk_mq_init_queue() so
the check needs to be updated as well.

Fixes: ffc771b3 ('mtip32xx: convert to use blk-mq')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Jens Axboe <axboe@fb.com>