HID: i2c-hid: move header file out of I2C realm

include/linux/i2c is not for client devices. Move the header file to a
more appropriate location.

Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Acked-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>