dio: Make dio_match_device() static

Unlike its PCI counterpart, dio_match_device() was never used outside
the DIO bus code.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Link: https://lore.kernel.org/r/20200112165613.20960-2-geert@linux-m68k.org