ARM: dts: kirkwood: synology: Fix rs5c372 RTC entry

In the rtc-rs5c372.c driver the compatible entry has been renamed
from rs5c372 to rs5c372a. Most dts files have been adapted.
This patch completes the change.

Signed-off-by: Walter Schweizer <ws.kernel@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>