HID: uclogic: Specify total report size to buttonpad macro

Simplify the UCLOGIC_RDESC_BUTTONPAD_BYTES macro by passing as param
the size of the report to pad to in bytes.

Signed-off-by: Nikolai Kondrashov <spbnick@gmail.com>
Signed-off-by: José Expósito <jose.exposito89@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>