crypto: geniv - use memcpy_sglist() instead of null skcipher

For copying data between two scatterlists, just use memcpy_sglist()
instead of the so-called "null skcipher".  This is much simpler.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

include/crypto/internal/geniv.h

@@ -15,7 +15,6 @@
 struct aead_geniv_ctx {
 	spinlock_t lock;
 	struct crypto_aead *child;
-	struct crypto_sync_skcipher *sknull;
 	u8 salt[] __attribute__ ((aligned(__alignof__(u32))));
 };