ARM: dts: stm32: set HSE_RTC clock frequency to 1 MHz on stm32f746

This patch set HSE_RTC clock frequency to 1 MHz, as the clock supplied to
the RTC must be 1 MHz.
Signed-off-by: Amelie Delaunay <amelie.delaunay@st.com>
Signed-off-by: Alexandre TORGUE <alexandre.torgue@st.com>

arch/arm/boot/dts/stm32f746.dtsi

@@ -320,6 +320,8 @@ rcc: rcc@40023800 {
 			reg = <0x40023800 0x400>;
 			clocks = <&clk_hse>, <&clk_i2s_ckin>;
 			st,syscfg = <&pwrcfg>;
+			assigned-clocks = <&rcc 1 CLK_HSE_RTC>;
+			assigned-clock-rates = <1000000>;
 		};
 	};
 };