powerpc/pseries/hotplug-memory: Change rc variable to bool

Changes the return variable to bool (as the return value) and
avoids doing a ternary operation before returning.

Signed-off-by: Leonardo Bras <leonardo@linux.ibm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20190802133914.30413-1-leonardo@linux.ibm.com