net: dm9051: Fix use after free in dm9051_loop_tx()

This code dereferences "skb" after calling dev_kfree_skb().

Fixes: 2dc95a4d

 ("net: Add dm9051 driver")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/r/20220221105440.GA10045@kili
Signed-off-by: Jakub Kicinski <kuba@kernel.org>