powerpc: Fix compile error with binutils 2.15

My previous patch to fix compilation with binutils-2.17 causes
a "file truncated" build error from ld with binutils 2.15 (and
possibly older), and a warning with 2.16 and 2.17.

This fixes it.

Signed-off-by: Segher Boessenkool <segher@kernel.crashing.org>
Acked-by: Chuck Meade <chuckmeade@mindspring.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>