ARM: dts: mmp3-dell-ariel: Add a name to /memory node

Ponted out by DTC:

  <stdout>: Warning (unit_address_vs_reg): /memory: node has a reg or ranges
  property, but no unit name

Link: https://lore.kernel.org/r/20191031163455.1711872-4-lkundrak@v3.sk


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