HID: i2c-hid: use helpers to do endian conversion in i2c_hid_get_input()

It is better to use helpers to do endian conversion as it documents
and draws attention to it, and might be a bit more performant as
well.

Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Tested-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>