ARM: dts: stm32: fix spi1 pin assignment on stm32mp15

Bank A and B IOs can't be handled by the pin controller 'Z'. This patch
assign spi1 pin definition to the correct controller.

Fixes: 9ad65d24 ("ARM: dts: stm32: stm32mp15-pinctrl: add spi1-1 pinmux group")

Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>