HID: google: drop superfluous const before SIMPLE_DEV_PM_OPS()

SIMPLE_DEV_PM_OPS() already implies const for the type; drop the
extra modifier.

Fixes: eb1aac4c ("HID: google: add support tablet mode switch for Whiskers")
Signed-off-by: Jiri Kosina <jkosina@suse.cz>