HID: debugfs: wake up reading tasks upon event

Some devices poke the hid core in a way that causes hid_debug_event to
be called, while never calling hid_dump_input. Without this wakeup
addition, tasks reading for hid events through debugfs may never see any
events. It may be that a well written driver doesn't cause this, but
then what's the point of debugfs?

Signed-off-by: Chase Douglas <chase.douglas@canonical.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>