ARM: dts: stm32: fix stm32mp157c-odyssey card detect pin

The microSD card detect pin is physically connected to the MPU pin PI3.
The Device Tree configuration of the card detect pin was wrong—it was
set to pin PB7 instead. If such configuration was used, the kernel would
hang on “Waiting for root device” when booting from a microSD card.

Signed-off-by: Grzegorz Szymaszek <gszymaszek@short.pl>
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>