net: sched: cls_flower: Fix an error code in fl_tmplt_create()

We forgot to set the error code on this path, so we return NULL instead
of an error pointer.  In the current code kzalloc() won't fail for small
allocations so this doesn't really affect runtime.

Fixes: b95ec7eb

 ("net: sched: cls_flower: implement chain templates")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>