HID: asus: Only set EV_REP if we are adding a mapping

Make asus_input_mapping() only set EV_REP if we are adding a mapping.

The T100CHI bluetooth keyboard dock has a few input reports for which
we do not create any mappings (these input-reports are present in the
descriptors but never send).

The hid-asus code relies on the HID core not creating input devices for
input-reports without any mappings. But the present of the EV_REP but
counts as a mapping causing 6 /dev/input/event# nodes to be created for
the T100CHI bluetooth keyboard dock. This change brings the amount of
created /dev/input/event# nodes / input-devices down to 4.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>