rtc: interface: fix kerneldoc comments

rtc: interface: fix kerneldoc comments

Fix kerneldoc warnings:

drivers/rtc/interface.c:619: warning: Function parameter or member 'num' not described in 'rtc_handle_legacy_irq'
drivers/rtc/interface.c:619: warning: Function parameter or member 'mode' not described in 'rtc_handle_legacy_irq'
drivers/rtc/interface.c:804: warning: Function parameter or member 'rtc' not described in 'rtc_timer_enqueue'
drivers/rtc/interface.c:804: warning: Function parameter or member 'timer' not described in 'rtc_timer_enqueue'
drivers/rtc/interface.c:864: warning: Function parameter or member 'rtc' not described in 'rtc_timer_remove'
drivers/rtc/interface.c:864: warning: Function parameter or member 'timer' not described in 'rtc_timer_remove'
drivers/rtc/interface.c:900: warning: Function parameter or member 'work' not described in 'rtc_timer_do_work'
drivers/rtc/interface.c:1035: warning: Function parameter or member 'rtc' not described in 'rtc_read_offset'
drivers/rtc/interface.c:1035: warning: Function parameter or member 'offset' not described in 'rtc_read_offset'
drivers/rtc/interface.c:1070: warning: Function parameter or member 'rtc' not described in 'rtc_set_offset'
drivers/rtc/interface.c:1070: warning: Function parameter or member 'offset' not described in 'rtc_set_offset'

Link: https://lore.kernel.org/r/20191127082932.666869-1-alexandre.belloni@bootlin.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>