crypto: x86/aes-gcm-vaes-avx2 - initialize full %rax return register

Update aes_gcm_dec_final_vaes_avx2() to be consistent with
aes_gcm_dec_final_aesni() and aes_gcm_dec_final_vaes_avx512() by
initializing the full %rax return register instead of just %al.
Technically this is unnecessary, since these functions return bool.  But
I think it's worth being extra careful with the result of the tag
comparison and also keeping the different implementations consistent.

Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20251102015256.171536-1-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>

arch/x86/crypto/aes-gcm-vaes-avx2.S

@@ -1123,6 +1123,7 @@ SYM_FUNC_END(aes_gcm_aad_update_vaes_avx2)
 	lea		.Lselect_high_bytes_table(%rip), %rax
 	vmovdqu		(%rax, TAGLEN64), %xmm1
 	vpshufb		BSWAP_MASK, %xmm1, %xmm1 // select low bytes, not high
+	xor		%eax, %eax
 	vptest		%xmm1, %xmm0
 	sete		%al
 .endif