rtc: sysfs: fix hctosys_show kerneldoc

Fix undocumented function parameters:
drivers/rtc/sysfs.c:112: warning: Function parameter or member 'dev' not described in 'hctosys_show'
drivers/rtc/sysfs.c:112: warning: Function parameter or member 'attr' not described in 'hctosys_show'
drivers/rtc/sysfs.c:112: warning: Function parameter or member 'buf' not described in 'hctosys_show'

Link: https://lore.kernel.org/r/20191122102212.400158-2-alexandre.belloni@bootlin.com


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>