rtc: vr41xx: Wire up alarm_irq_enable

drivers/rtc/rtc-vr41xx.c:229: warning: ‘vr41xx_rtc_alarm_irq_enable’ defined but not used

Apparently the conversion to alarm_irq_enable forgot to wire up the
callback.

Fixes: 16380c15

 ("RTC: Convert rtc drivers to use the alarm_irq_enable method")
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>