rtc: sa1100: DT spelling s/interrupt-name/interrupt-names/

Fix typo in interrupt-names

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>