Fix typo in x86_64-mont5.pl CFI directives

Reviewed-by: Kurt Roeckx <kurt@openssl.org>
Reviewed-by: Andy Polyakov <appro@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2655)

crypto/bn/asm/x86_64-mont5.pl

diff --git a/crypto/bn/asm/x86_64-mont5.pl b/crypto/bn/asm/x86_64-mont5.pl
index 7ed2232..9c77642 100755
--- a/crypto/bn/asm/x86_64-mont5.pl
+++ b/crypto/bn/asm/x86_64-mont5.pl
@@ -120,7 +120,7 @@
 	push	%r14
 .cfi_push	%r14
 	push	%r15
-.cfi_push	%r14
+.cfi_push	%r15
 
 	neg	$num
 	mov	%rsp,%r11