HID: intel-ish-hid: Send clock sync message immediately after reset

The ISH driver performs a clock sync with the firmware once at system
startup and then every 20 seconds. If a firmware reset occurs right
after a clock sync, the driver would wait 20 seconds before performing
another clock sync with the firmware. This is particularly problematic
with the introduction of the "load firmware from host" feature, where
the driver performs a clock sync with the bootloader and then has to
wait 20 seconds before syncing with the main firmware.

This patch clears prev_sync immediately upon receiving an IPC reset,
so that the main firmware and driver will perform a clock sync
immediately after completing the IPC handshake.

Signed-off-by: Zhang Lixu <lixu.zhang@intel.com>
Acked-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Jiri Kosina <jkosina@suse.com>