platform/chrome: cros_ec_ishtp: fix crash during suspend

Kernel crashes during suspend due to wrong conversion in
suspend and resume functions.

Use the proper helper to get ishtp_cl_device instance.

Cc: <stable@vger.kernel.org> # 5.2.x: b12bbdc5: HID: intel-ish-hid: fix wrong driver_data usage
Signed-off-by: Hyungwoo Yang <hyungwoo.yang@intel.com>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>