HID: intel-ish-hid: Simplify logic in ishtp_cl_device_remove()

There is only a single change in behavior: Now dev->driver isn't modified.
Assigning to this variable is in the domain of the driver core only. (And
it's done in __device_release_driver shortly after bus->remove() (i.e
ishtp_cl_device_remove() here) returns.)

Signed-off-by: Uwe Kleine-König <uwe@kleine-koenig.org>
Acked-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>