isci: cleanup isci_remote_device[_not]_ready interface

Require a valid isci_host in support of the general cleanup to not
re-lookup the host via potentially fragile methods when more robust
methods are available.  Also cleans up some more casting that should be
using container_of() to up-cast a base structure in a more type-safe
manner.

Signed-off-by: Dan Williams <dan.j.williams@intel.com>