Restore |xmm7| correctly on Win64 in aesni-gcm-x86_64.

See OpenSSL df057ea6c8.

Change-Id: Ife10dc13ca335cd51434d7769ff85c6929f10226
Reviewed-on: https://boringssl-review.googlesource.com/7172
Reviewed-by: David Benjamin <davidben@google.com>

crypto/modes/asm/aesni-gcm-x86_64.pl

@@ -477,7 +477,7 @@ $code.=<<___;
 ___
 $code.=<<___ if ($win64);
 	movaps	-0xd8(%rax),%xmm6
-	movaps	-0xd8(%rax),%xmm7
+	movaps	-0xc8(%rax),%xmm7
 	movaps	-0xb8(%rax),%xmm8
 	movaps	-0xa8(%rax),%xmm9
 	movaps	-0x98(%rax),%xmm10