net: dsa: mv88e6xxx: wait for 88E6185 PPU disabled

The PPU state of 88E6185 can be either "Disabled at Reset" or
"Disabled after Initialization". Because we intentionally clear the
PPU Enabled bit before checking its state, it is safe to wait for the
MV88E6185_G1_STS_PPU_STATE_DISABLED state explicitly instead of waiting
for any state different than MV88E6185_G1_STS_PPU_STATE_POLLING.

Signed-off-by: Vivien Didelot <vivien.didelot@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>