i40e: Use signed variable

The counter variable in i40e_clean_tx_irq starts out negative and climbs
to 0. So it should not be defined as a u16. This was working by accident
due to the fact the u16 overflows and underflows predictably.

Replace the u16 with int, which is signed and can handle the negativity.
Signed-off-by: Mitch Williams <mitch.a.williams@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/i40e/i40e_txrx.c

@@ -774,7 +774,7 @@ void i40e_detect_recover_hung(struct i40e_vsi *vsi)
 static bool i40e_clean_tx_irq(struct i40e_vsi *vsi,
 			      struct i40e_ring *tx_ring, int napi_budget)
 {
-	u16 i = tx_ring->next_to_clean;
+	int i = tx_ring->next_to_clean;
 	struct i40e_tx_buffer *tx_buf;
 	struct i40e_tx_desc *tx_head;
 	struct i40e_tx_desc *tx_desc;