fix compilation error in arch/ppc/syslib/open_pic_defs.h

make defconfig give the following error on ppc (gcc-4):

arch/ppc/syslib/open_pic.c:36: error: static declaration of ‘OpenPIC’ follows non-static declaration arch/ppc/syslib/open_pic_defs.h:175: error: previous declaration of ‘OpenPIC’ was here

The following patch solves it.

@@ -172,9 +172,6 @@ struct OpenPIC {
     OpenPIC_Processor Processor[OPENPIC_MAX_PROCESSORS];
 };
 
-extern volatile struct OpenPIC __iomem *OpenPIC;
-
-
     /*
      *  Current Task Priority Register
      */