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>

arch/powerpc/mm/tlb_nohash_low.S

@@ -191,6 +191,6 @@ ALT_MMU_FTR_SECTION_END_IFCLR(MMU_FTR_USE_TLBILX)
 	isync
 1:	wrtee	r10
 	blr
-#elif
+#else
 #error Unsupported processor type !
 #endif