powerpc: Remove big endianness assumption in of_find_next_cache_node

Currently big endianness of the device tree data is assumed in
of_find_next_cache_node for 'handle' when calling of_find_node_by_phandle.

In preparation to move this function to common code, this patch fixes
the endianness using 'be32_to_cpup'

Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Grant Likely <grant.likely@linaro.org>
Cc: Rob Herring <rob.herring@calxeda.com>
Signed-off-by: Sudeep KarkadaNagesha <sudeep.karkadanagesha@arm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>