ARM: dts: mmp3: Add a name to /clocks node

It should have one and DTC is indeed unhappy about its absence:

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

Link: https://lore.kernel.org/r/20191031163455.1711872-2-lkundrak@v3.sk


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