arm64: dts: imx8mm-kontron: Fix interrupt for RTC on OSM-S i.MX8MM module

[ Upstream commit 8d0f39b7 ]

The level of the interrupt signal is active low instead. Fix this.

Fixes: de9618e8 ("arm64: dts: Add support for Kontron SL/BL i.MX8MM OSM-S")
Signed-off-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>