ARM: dts: stm32: Fix qspi pinctrl phandle for stm32mp15xx-dhcor-som

Chip select pinctrl phandle was missing in several stm32mp15x based boards.

Fixes: ea99a5a0

 ("ARM: dts: stm32: Create separate pinmux for qspi cs pin in stm32mp15-pinctrl.dtsi")

Signed-off-by: Patrice Chotard <patrice.chotard@foss.st.com>
Cc: Marek Vasut <marex@denx.de>
Cc: Alexandre Torgue <alexandre.torgue@st.com>
Cc: linux-stm32@st-md-mailman.stormreply.com
Cc: linux-arm-kernel@lists.infradead.org
Reviewed-by: Marek Vasut <marex@denx.de>
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>