ARM: dts: stm32: Fix GPIO hog flags on DHCOM PicoITX

The GPIO hog flags are ignored by gpiolib-of.c now, set the flags to 0.
Due to a change in gpiolib-of.c, setting flags to GPIO_ACTIVE_LOW and
using output-low DT property leads to the GPIO being set high instead.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Patrice Chotard <patrice.chotard@st.com>
Cc: Patrick Delaunay <patrick.delaunay@st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@st.com>
Reviewed-by: Patrick Delaunay <patrick.delaunay@foss.st.com>