IB/srp: Release transport before removing host

The documented call sequence for removing a host is to call the
transport xxx_remove_host() prior to scsi_remove_host(). The SRP
transport used to crash when that order was followed, but as it is now
fixed, use the documented order.

Signed-off-by: David Dillow <dillowda@ornl.gov>
Acked-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: Roland Dreier <rolandd@cisco.com>