ARM: dts: stm32: Fix AV96 eMMC pinmux

Commit 500327e2 ("ARM: dts: stm32mp1: DT alignment with Linux kernel v5.8-rc1")
renamed sdmmc2_d47_pins_b phandle to sdmmc2_d47_pins_c, but without updating
the AV96 DT which uses that phandle. Linux missed similar update as well and
it was only added in commit 1ad6e36ec266 ("ARM: dts: stm32: Fix sdmmc2 pins
on AV96") .

Update the AV96 DT pinmux phandle, otherwise eMMC 8bit mode does not work
and access to eMMC takes a very long time to fall back to 4bit mode.
Signed-off-by: NMarek Vasut <marex@denx.de>
Cc: Patrick Delaunay <patrick.delaunay@foss.st.com>
Cc: Patrice Chotard <patrice.chotard@foss.st.com>
Reviewed-by: NPatrick Delaunay <patrick.delaunay@foss.st.com>

arch/arm/dts/stm32mp15xx-dhcor-avenger96-u-boot.dtsi

@@ -57,7 +57,7 @@
 	};
 };
 
-&sdmmc2_d47_pins_b {
+&sdmmc2_d47_pins_c {
 	u-boot,dm-spl;
 	pins {
 		u-boot,dm-spl;

arch/arm/dts/stm32mp15xx-dhcor-avenger96.dts

@@ -152,7 +152,7 @@
 
 &sdmmc2 {
 	pinctrl-names = "default";
-	pinctrl-0 = <&sdmmc2_b4_pins_a &sdmmc2_d47_pins_b>;
+	pinctrl-0 = <&sdmmc2_b4_pins_a &sdmmc2_d47_pins_c>;
 	non-removable;
 	no-sd;
 	no-sdio;