crypto: x86/nh-avx2 - add missing vzeroupper

Since nh_avx2() uses ymm registers, execute vzeroupper before returning
from it.  This is necessary to avoid reducing the performance of SSE
code.

Fixes: 0f961f9f ("crypto: x86/nhpoly1305 - add AVX2 accelerated NHPoly1305")
Signed-off-by: Eric Biggers <ebiggers@google.com>
Acked-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

arch/x86/crypto/nh-avx2-x86_64.S

@@ -154,5 +154,6 @@ SYM_TYPED_FUNC_START(nh_avx2)
 	vpaddq		T1, T0, T0
 	vpaddq		T4, T0, T0
 	vmovdqu		T0, (HASH)
+	vzeroupper
 	RET
 SYM_FUNC_END(nh_avx2)