net: ag71xx: Slightly simplify 'ag71xx_rx_packets()'

There is no need to use 'list_for_each_entry_safe' here, as nothing is
removed from the list in the 'for' loop.
Use 'list_for_each_entry' instead, it is slightly less verbose.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>