powerpc/pseries: Fix over writing of rtas return code in update_dt_node

The rc variable is initially used to store the return code from the
ibm,update-properties rtas call which returns 0 or 1 on success. A return
code of 1 indicates that ibm,update-properties must be called again for the
node. However, the rc variable is overwritten by a call to update_dt_prop
which returns 0 on success. This results in ibm,update-properties not being
called again for the given node when the rtas call rc was previously 1.

Signed-off-by: Tyrel Datwyler <tyreld@linux.vnet.ibm.com>
Acked-by: Nathan Fontenot <nfont@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>