qla2xxx: Fix shost use-after-free on device removal

Once calling scsi_host_put, be careful to not access qla_hw_data through
the Scsi_Host private data (ie, scsi_qla_host base_vha).

Fixes: fe1b806f ("qla2xxx: Refactor shutdown code so some functionality can be reused")
Cc: stable@vger.kernel.org # 3.14, 3.15, 3.16
Signed-off-by: Joe Lawrence <joe.lawrence@stratus.com>
Acked-by: Chad Dupuis <chad.dupuis@qlogic.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>