[CRYPTO] hmac: Fix hmac_init update call

The crypto_hash_update call in hmac_init gave the number 1
instead of the length of the sg list in bytes.  This is a
missed conversion from the digest => hash change.

As tcrypt only tests crypto_hash_digest it didn't catch this.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>