crypto: aesni - fix typo in generic_gcmaes_decrypt

generic_gcmaes_decrypt needs to use generic_gcmaes_ctx, not
aesni_rfc4106_gcm_ctx. This is actually harmless because the fields in
struct generic_gcmaes_ctx share the layout of the same fields in
aesni_rfc4106_gcm_ctx.

Fixes: cce2ea8d ("crypto: aesni - add generic gcm(aes)")
Cc: <stable@vger.kernel.org>
Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
Reviewed-by: Stefano Brivio <sbrivio@redhat.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>