HID: intel-ish-hid: use helper function to search client id

ishtp exposed helper ishtp_fw_cl_get_client() function for client
information searching, so switch to use it.

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>