bn/asm/rsaz-avx2.pl: fix occasional failures.
diff --git a/crypto/bn/asm/rsaz-avx2.pl b/crypto/bn/asm/rsaz-avx2.pl
index dd83ed6..931dd5a 100755
--- a/crypto/bn/asm/rsaz-avx2.pl
+++ b/crypto/bn/asm/rsaz-avx2.pl
@@ -991,6 +991,7 @@
 
 	vmovdqu	.Land_mask(%rip), $AND_MASK
 	mov	\$9, $i
+	vmovdqu	$ACC9, 32*9-128($rp)		# $ACC9 is zero after vzeroall
 	jmp	.Loop_mul_1024
 
 .align	32