arch/powerpc/platforms/pseries/hotplug-memory.c: fix section handling code

Fix

  arch/powerpc/platforms/pseries/hotplug-memory.c: In function 'pseries_remove_memblock':
  arch/powerpc/platforms/pseries/hotplug-memory.c:103:17: error: unused variable 'pfn' [-Werror=unused-variable]

Caused by commit d760afd4 ("memory-hotplug: suppress "Trying to free
nonexistent resource <XXXXXXXXXXXXXXXX-YYYYYYYYYYYYYYYY>" warning").

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Tested-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: Nathan Fontenot <nfont@linux.vnet.ibm.com>
Tested-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>