of/resolver: Simplify to be32_add_cpu()

This is the same as be32_add_cpu(), so simplify the code and
remove the now unused local variable.

Signed-off-by: Stephen Boyd <stephen.boyd@linaro.org>
Reviewed-by: Frank Rowand <frowand.list@gmail.com>
Signed-off-by: Rob Herring <robh@kernel.org>