ARM: scu: mask cluster id from cpu_logical_map

With commit a0ae0240

 (ARM: kernel: add device tree init map function),
the cpu id value may include the cluster id and is no longer 0-3, so we
need to mask it in scu_power_mode to get the local cpu number. Since we
are only dealing with the cpu we are running on, the cluster id should
not ever be needed.

Signed-off-by: Rob Herring <rob.herring@calxeda.com>