ARM: dts: stm32: Fix sdmmc2 pins on AV96

The AV96 uses sdmmc2_d47_pins_c and sdmmc2_d47_sleep_pins_c, which
differ from sdmmc2_d47_pins_b and sdmmc2_d47_sleep_pins_b in one
pin, SDMMC2_D5, which is PA15 in the former and PA9 in the later.
The PA15 is correct on AV96, so fix this. This error is likely a
result of rebasing across the stm32mp1 DT pinctrl rework.

Fixes: 611325f6 ("ARM: dts: stm32: Add eMMC attached to SDMMC2 on AV96")
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Alexandre Torgue <alexandre.torgue@st.com>
Cc: Maxime Coquelin <mcoquelin.stm32@gmail.com>
Cc: Patrice Chotard <patrice.chotard@st.com>
Cc: Patrick Delaunay <patrick.delaunay@st.com>
Cc: linux-stm32@st-md-mailman.stormreply.com
To: linux-arm-kernel@lists.infradead.org
Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>