powerpc/pseries: Fix dlpar compile warning without CONFIG_PROC_DEVICETREE

cc1: warnings being treated as errors
arch/powerpc/platforms/pseries/dlpar.c: In function 'dlpar_attach_node':
arch/powerpc/platforms/pseries/dlpar.c:239: error: unused variable 'ent'
arch/powerpc/platforms/pseries/dlpar.c: In function 'dlpar_detach_node':
arch/powerpc/platforms/pseries/dlpar.c:271: error: unused variable 'prop'
arch/powerpc/platforms/pseries/dlpar.c:270: error: unused variable 'parent'
make[3]: *** [arch/powerpc/platforms/pseries/dlpar.o] Error 1

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>