[POWERPC] Fix a compiler warning in mm/tlb_64.c

The compiler doesn't understand that BUG() never returns, so complains that
psize isn't set. Just set it to the normal value, which seems to produce nice
code and keeps gcc happy.
Signed-off-by: NMichael Ellerman <michael@ellerman.id.au>
Signed-off-by: NStephen Rothwell <sfr@canb.auug.org.au>

arch/powerpc/mm/tlb_64.c

@@ -146,6 +146,7 @@ void hpte_update(struct mm_struct *mm, unsigned long addr,
 		psize = mmu_huge_psize;
 #else
 		BUG();
+		psize = pte_pagesize_index(pte); /* shutup gcc */
 #endif
 	} else
 		psize = pte_pagesize_index(pte);