rtc: don't reference bogus function pointer in kdoc

The mentioned function pointer is long gone since early 2011. Remove the
reference in the comment and reword it slightly.

Fixes: 51ba60c5bb3b ("RTC: Cleanup rtc_class_ops->update_irq_enable()")
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
1 file changed