net/act_pedit: fix an error code

net/act_pedit: fix an error code

I'm reviewing static checker warnings where we do ERR_PTR(0), which is
the same as NULL.  I'm pretty sure we intended to return ERR_PTR(-EINVAL)
here.  Sometimes these bugs lead to a NULL dereference but I don't
immediately see that problem here.

Fixes: 71d0ed7079df ("net/act_pedit: Support using offset relative to the conventional network headers")
Signed-off-by: Dan Carpenter <[email protected]>
Acked-by: Amir Vadai <[email protected]>
Signed-off-by: David S. Miller <[email protected]>