m68k: m68328: use legacy_timer_tick()

A couple of machines share the m68328 timer code that
is based on calling timer_interrupt(). Change these
to the new and slightly more generic legacy_timer_tick()
helper.

Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>