powerpc/powernv: Fix little endian issues in OPAL error log code

Fix little endian issues with the OPAL error log code.

Signed-off-by: Anton Blanchard <anton@samba.org>
Reviewed-by: Stewart Smith <stewart@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>