ARM: dts: mmp3: Fix /soc/watchdog node name

There's a typo there that rightfully upsets DTS:

  <stdout>: Warning (simple_bus_reg): /soc/watchdog@2c000620: simple-bus
  unit address format error, expected "e0000620"

Link: https://lore.kernel.org/r/20191031163455.1711872-3-lkundrak@v3.sk


Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Signed-off-by: Olof Johansson <olof@lixom.net>