edac: cpc925: use for_each_of_cpu_node iterator

Use the for_each_of_cpu_node iterator to iterate over cpu nodes. This
has the side effect of defaulting to iterating using "cpu" node names in
preference to the deprecated (for FDT) device_type == "cpu".

The error messages are removed in the process as it's not the driver's
job to be checking cpu nodes. Any problems with cpu nodes should be
noticed by the architecture code.

Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: linux-edac@vger.kernel.org
Acked-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Rob Herring <robh@kernel.org>