ARM: dts: stm32: Drop nWP GPIO hog on DHSOM

The nWP GPIO hog was used to unlock the SPI NOR write protect when U-Boot
used to operate the SPI NOR in 1-1-1 mode. Now that the SPI NOR is operated
in 1-1-4 mode, the hog has adverse effects and causes transfer corruption,
since the hogged pin is also the IO2 pin. Remove the hogs.

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