staging: mt7621-dts: allow gnubee to reboot cleanly.

Since commit bb276262 ("mtd: spi-nor: only apply reset hacks to
broken hardware"), we need to mark the spi-nor as "broken" for reboot
to work.
Note that nothing is actually broken here.  The hardware-watchdog in
the SoC isn't wired in a way that works, but then the board doesn't
claim to support a hardware watchdog - and the SPI certain isn't
"broken".

This causes an annoying warning on every boot, but that is better than
failing on ever reboot.

Signed-off-by: NeilBrown <neil@brown.name>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>