rtc: st: Update IP layout information to include Clocksource

Initial submission adding support for this IP only included Watchdog and
the Real-Time Clock. Now the third (and final) device is enabled this
trivial patch is required to update the comment in the RTC driver to
encompass Clocksource.

Acked-by: Alexandre Belloni <[e-mail]>
Signed-off-by: Lee Jones <[e-mail]>

drivers/rtc/rtc-st-lpc.c

···
 		return -EINVAL;
 	}
 
-	/* LPC can either run in RTC or WDT mode */
+	/* LPC can either run as a Clocksource or in RTC or WDT mode */
 	if (mode != ST_LPC_MODE_RTC)
 		return -ENODEV;