HID: intel_ish-hid: convert timespec to ktime_t

The internal accounting uses 'timespec' based time stamps, which is
slightly inefficient and also problematic once we get to the time_t
overflow in 2038.

When communicating to the firmware, we even get an open-coded 64-bit
division that prevents the code from being build-tested on 32-bit
architectures and is inefficient due to the double conversion from
64-bit nanoseconds to seconds+nanoseconds and then microseconds.

This changes the code to use ktime_t instead.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>