HID: intel-ish-hid: use helper function for private driver data set/get

Use helper set/get function to set/get driver data in ishtp-hid-client
driver instead of directly accessing cl_device driver_data member.

Signed-off-by: Even Xu <even.xu@intel.com>
Reviewed-by: Andriy Shevchenko <andriy.shevchenko@intel.com>
Acked-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>