HID: i2c-hid: force the IRQ level trigger only when not set

Instead of forcing the level trigger of the IRQ, we can count
on ACPI or OF to set it up for us.

The first release of the HID over I2C specification mentioned
that the level trigger needed to be active low. In the latest
version of the specification, there is no such explicit mention,
so it's better to not assume one.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>