boards: stm32n6570_dk: Assign XSPI1 clock to HCLK

Due to a BootROM clock switching issue, XSPI1 should use HCLK otherwise
app won't restart on reset.

Signed-off-by: Erwan Gouriou <erwan.gouriou@st.com>

Author: erwango

boards/st/stm32n6570_dk/stm32n6570_dk_common.dtsi

@@ -295,7 +295,7 @@ zephyr_udc0: &usbotg_hs1 {
 		     &xspim_p1_io15_pp15>;
 	pinctrl-names = "default";
 	clocks = <&rcc STM32_CLOCK(AHB5, 5)>,
-		 <&rcc STM32_SRC_IC3 XSPI1_SEL(2)>,
+		 <&rcc STM32_SRC_HCLK5 XSPI1_SEL(0)>,
 		 <&rcc STM32_CLOCK(AHB5, 13)>;
 	status = "okay";