PM: fix compiler error of PPC dart_iommu

A dummy inline function of register_nosave_region_late was accidentally
removed by the recent PM patch that introduced suspend notifiers.
This elimination causes the following compiler error on PPC machines.

  CC      arch/powerpc/sysdev/dart_iommu.o
arch/powerpc/sysdev/dart_iommu.c: In function 'iommu_init_late_dart':
arch/powerpc/sysdev/dart_iommu.c:376: error: implicit declaration of function
'register_nosave_region_late'
make[1]: *** [arch/powerpc/sysdev/dart_iommu.o] Error 1
make: *** [arch/powerpc/sysdev] Error 2

This patch fixes the problem.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Acked-by: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>