rtc: rtc-ds1307: enable support for mcp794xx as a wakeup source without IRQ

This patch extends the fixes for ds1337, ds1339, ds3231 in commit
8bc2a40730ec ("rtc: ds1307: add support for the DT property
'wakeup-source'") to mcp794xx devices, so that those parts can similarly be
used as a wakeup source without an IRQ to the processor.

Tested on Raspberry Pi ZeroW with MCP79400.

Signed-off-by: David Lowe <dave-lowe@ntlworld.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>

drivers/rtc/rtc-ds1307.c

@@ -1407,7 +1407,8 @@ static int ds1307_probe(struct i2c_client *client,
 		break;
 	case mcp794xx:
 		rtc_ops = &mcp794xx_rtc_ops;
-		if (ds1307->irq > 0 && chip->alarm) {
+		if (chip->alarm && (ds1307->irq > 0 ||
+				    ds1307_can_wakeup_device)) {
 			irq_handler = mcp794xx_irq;
 			want_irq = true;
 		}