HID: intel-ish-hid: using list_head for ipc write queue

Currently wr_msg_ctl_info is used in ishtp_device just for list head
purpose, using list_head directly can save ~150 bytes size for
each replacement.

Also this patch can save ~170 bytes of code size in intel-ish-ipc.ko.

Signed-off-by: Hong Liu <hong.liu@intel.com>
Acked-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>