powerpc: fix for long standing bug noticed by gcc 4.4.0

Previous gcc versions didn't notice this because one of the preceding
#ifs always evaluated to true.

gcc 4.4.0 produced this error:

arch/powerpc/mm/tlb_nohash_low.S:206:6: error: #elif with no expression

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Acked-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>