powerpc/32s: fix flush_hash_pages() on SMP

flush_hash_pages() runs with data translation off, so current
task_struct has to be accesssed using physical address.

Fixes: f7354cca ("powerpc/32: Remove CURRENT_THREAD_INFO and rename TI_CPU")
Cc: stable@vger.kernel.org # v5.1+
Reported-by: Erhard F. <erhard_f@mailbox.org>
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/mm/book3s32/hash_low.S

@@ -539,7 +539,8 @@ _GLOBAL(flush_hash_pages)
 #ifdef CONFIG_SMP
 	lis	r9, (mmu_hash_lock - PAGE_OFFSET)@ha
 	addi	r9, r9, (mmu_hash_lock - PAGE_OFFSET)@l
-	lwz	r8,TASK_CPU(r2)
+	tophys	(r8, r2)
+	lwz	r8, TASK_CPU(r8)
 	oris	r8,r8,9
 10:	lwarx	r0,0,r9
 	cmpi	0,r0,0