powerpc: 32 bit getcpu VDSO function uses 64 bit instructions

I used some 64 bit instructions when adding the 32 bit getcpu VDSO
function. Fix it.

Fixes: 18ad51dd ("powerpc: Add VDSO version of getcpu")
Cc: stable@vger.kernel.org
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>