arm64: dts: imx8mn: add clock for snvs rtc node

Initial commit adding imx8mn support:
6c3debcb ("arm64: dts: freescale: Add i.MX8MN dtsi support")
added the "clock-names" property for the snvs rtc node,
however it missed adding the clock.
Signed-off-by: Horia Geantă <horia.geanta@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm64/boot/dts/freescale/imx8mn.dtsi

@@ -358,6 +358,7 @@ snvs_rtc: snvs-rtc-lp {
 					offset = <0x34>;
 					interrupts = <GIC_SPI 19 IRQ_TYPE_LEVEL_HIGH>,
 						     <GIC_SPI 20 IRQ_TYPE_LEVEL_HIGH>;
+					clocks = <&clk IMX8MN_CLK_SNVS_ROOT>;
 					clock-names = "snvs-rtc";
 				};