IB/srp: Fix list corruption/oops on module reload

Add a missing call to srp_remove_host() in srp_remove_one() so that we 
don't leak SRP transport class list entries.

Tested-by: David Dillow <dillowda@ornl.gov>
Acked-by: FUJITA Tomonori <tomof@acm.org>
Signed-off-by: Roland Dreier <rolandd@cisco.com>