MN10300: Use clockevents_calc_mult_shift()

Use clockevents_calc_mult_shift() instead of the homebrewn function in
mn10300/kernel/time.c.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: John Stultz <johnstul@us.ibm.com>
Cc: Koichi Yasutake <yasutake.koichi@jp.panasonic.com>
Cc: Mark Salter <msalter@redhat.com>
Signed-off-by: David Howells <dhowells@redhat.com>