m68k: coldfire: use legacy_timer_tick()

Replace the indirect function calls in the timer code
with direct calls to the newly added legacy_timer_tick()
helper for those that have not yet been converted to
generic clockevents.

This makes the timer code a little more self-contained.

Tested-by: Greg Ungerer <gerg@linux-m68k.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>