netdevsim: fix unbalaced locking in nsim_create()

In the nsim_create(), rtnl_lock() is called before nsim_bpf_init().
If nsim_bpf_init() is failed, rtnl_unlock() should be called,
but it isn't called.
So, unbalanced locking would occur.

Fixes: e05b2d14 ("netdevsim: move netdev creation/destruction to dev probe")
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>