powerpc: fix compile error with 85xx/p1010rdb.c

Current linux-next compiled with mpc85xx_defconfig causes this:

arch/powerpc/platforms/85xx/p1010rdb.c:41:14: error: 'np' undeclared (first use in this function)
arch/powerpc/platforms/85xx/p1023_rds.c:102:14: error: 'np' undeclared (first use in this function)

Introduced in:
  commit 996983b7
  Author: Kyle Moffett <Kyle.D.Moffett@boeing.com>
  Date:   Fri Dec 2 06:28:02 2011 +0000
  powerpc/mpic: Search for open-pic device-tree node if NULL

Signed-off-by: Tony Breeds <tony@bakeyournoodle.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>