bn/asm/x86_64-mont5.pl: fix valgrind error.

bn_get_bits5 was overstepping array boundary by 1 byte. It was exclusively
read overstep and data could not have been used. The only potential problem
would be if array happens to end on the very edge of last accesible page.

Reviewed-by: Richard Levitte <levitte@openssl.org>
(cherry picked from commit 69567687b0)

crypto/bn/asm/x86_64-mont5.pl

@@ -3226,11 +3226,16 @@ $code.=<<___;
 .type	bn_get_bits5,\@abi-omnipotent
 .align	16
 bn_get_bits5:
-	mov	$inp,%r10
+	lea	0($inp),%r10
+	lea	1($inp),%r11
 	mov	$num,%ecx
-	shr	\$3,$num
-	movzw	(%r10,$num),%eax
-	and	\$7,%ecx
+	shr	\$4,$num
+	and	\$15,%ecx
+	lea	-8(%ecx),%eax
+	cmp	\$11,%ecx
+	cmova	%r11,%r10
+	cmova	%eax,%ecx
+	movzw	(%r10,$num,2),%eax
 	shrl	%cl,%eax
 	and	\$31,%eax
 	ret