sfc (gcc13): synchronize ef100_enqueue_skb()'s return type

ef100_enqueue_skb() generates a valid warning with gcc-13:
  drivers/net/ethernet/sfc/ef100_tx.c:370:5: error: conflicting types for 'ef100_enqueue_skb' due to enum/integer mismatch; have 'int(struct efx_tx_queue *, struct sk_buff *)'
  drivers/net/ethernet/sfc/ef100_tx.h:25:13: note: previous declaration of 'ef100_enqueue_skb' with type 'netdev_tx_t(struct efx_tx_queue *, struct sk_buff *)'

I.e. the type of the ef100_enqueue_skb()'s return value in the declaration is
int, while the definition spells enum netdev_tx_t. Synchronize them to the
latter.

Cc: Martin Liska <mliska@suse.cz>
Cc: Edward Cree <ecree.xilinx@gmail.com>
Cc: Martin Habets <habetsm.xilinx@gmail.com>
Signed-off-by: Jiri Slaby (SUSE) <jirislaby@kernel.org>
Link: https://lore.kernel.org/r/20221031114440.10461-1-jirislaby@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/sfc/ef100_tx.c

@@ -367,7 +367,8 @@ void ef100_ev_tx(struct efx_channel *channel, const efx_qword_t *p_event)
  * Returns 0 on success, error code otherwise. In case of an error this
  * function will free the SKB.
  */
-int ef100_enqueue_skb(struct efx_tx_queue *tx_queue, struct sk_buff *skb)
+netdev_tx_t ef100_enqueue_skb(struct efx_tx_queue *tx_queue,
+			      struct sk_buff *skb)
 {
 	return __ef100_enqueue_skb(tx_queue, skb, NULL);
 }