rtc: Allow child drivers

Some RTC chips have child drivers, e.g. to provide access to their
non-volatile RAM. Scan for these when binding.

Signed-off-by: Simon Glass <sjg@chromium.org>

drivers/rtc/rtc-uclass.c

@@ -122,4 +122,5 @@ int rtc_write32(struct udevice *dev, unsigned int reg, u32 value)
 UCLASS_DRIVER(rtc) = {
 	.name		= "rtc",
 	.id		= UCLASS_RTC,
+	.post_bind	= dm_scan_fdt_dev,
 };