[SCSI] iscsi class: fix endpoint leak

class_find_device gets a ref to the device so we must release it.
The class will serialize access to the ep so we do not have to worry
about a remove racing with the callers access, so we can simplify the
use and drop the ref right away.

Signed-off-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>