[NET]: Fix unbalanced rcu_read_unlock in __sock_create

The recent RCU work created an unbalanced rcu_read_unlock
in __sock_create.  This patch fixes that.  Reported by
oleg 123.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>