[PATCH] CHECKFLAGS on ppc64 got broken

Now that asm-powerpc/* is using ifdefs on __powerpc64__ we need to add it
to CHECKFLAGS on ppc64.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>