ARM: dts: imx6: phytec: fix RTC interrupt level

RTC interrupt level should be set to "LOW". This was revealed by the
introduction of commit:

  f181987e ("rtc: m41t80: use IRQ flags obtained from fwnode")

which changed the way IRQ type is obtained.
Signed-off-by: Andrej Picej <andrej.picej@norik.com>
Reviewed-by: Stefan Riedmüller <s.riedmueller@phytec.de>
Fixes: 800d5951 ("ARM: dts: imx6: Add initial support for phyBOARD-Mira")
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/boot/dts/nxp/imx/imx6qdl-phytec-mira.dtsi

@@ -182,7 +182,7 @@ i2c_rtc: rtc@68 {
 		pinctrl-0 = <&pinctrl_rtc_int>;
 		reg = <0x68>;
 		interrupt-parent = <&gpio7>;
-		interrupts = <8 IRQ_TYPE_LEVEL_HIGH>;
+		interrupts = <8 IRQ_TYPE_LEVEL_LOW>;
 		status = "disabled";
 	};
 };