rtc: sysfs: use __ATTRIBUTE_GROUPS()

Embrace __ATTRIBUTE_GROUPS() to avoid boiler plate code.
This should not introduce any functional changes.

Signed-off-by: Andy Shevchenko <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexandre Belloni <[e-mail]>

drivers/rtc/sysfs.c

···
 	.is_visible	= rtc_attr_is_visible,
 	.attrs		= rtc_attrs,
 };
-
-static const struct attribute_group *rtc_attr_groups[] = {
-	&rtc_attr_group,
-	NULL
-};
+__ATTRIBUTE_GROUPS(rtc_attr);
 
 const struct attribute_group **rtc_get_dev_attribute_groups(void)
 {