Revert "IB/srp: Avoid that a cable pull can trigger a kernel crash"

The caller of srp_ib_lookup_path() is responsible for holding a reference
on the SCSI host. That means that commit 8a0d18c6 was not necessary.
Hence revert it.

Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>