crypto: mxc-scc - fix unwinding in mxc_scc_crypto_register()

There are two issues here:

1) We need to decrement "i" otherwise we unregister something that was
   not successfully registered.
2) The original code did not unregister the first element in the array
   where i is zero.

Fixes: d293b640

 ('crypto: mxc-scc - add basic driver for the MXC SCC')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>