crypto: cryptd - use crypto_grab_shash() and simplify error paths

Make the cryptd template (in the hash case) use the new function
crypto_grab_shash() to initialize its shash spawn.

This is needed to make all spawns be initialized in a consistent way.

This required making cryptd_create_hash() allocate the instance directly
rather than use cryptd_alloc_instance().

Also simplify the error handling by taking advantage of crypto_drop_*()
now accepting (as a no-op) spawns that haven't been initialized yet, and
by taking advantage of crypto_grab_*() now handling ERR_PTR() names.

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