ice: Use the software based tail when checking for hung Tx ring

Currently in ice_get_tx_pending we try to read a Tx ring's tail. This is
then compared with the software based head (next_to_clean) to determine
if we have pending work. This will never work because reading of the Tx
ring's tail is no longer supported. Fix this by using the software based
tail (next_to_use) to determine if there is pending work.
Signed-off-by: NBrett Creeley <brett.creeley@intel.com>
Tested-by: NAndrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: NJeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/ice/ice_main.c

@@ -41,12 +41,12 @@ static void ice_update_pf_stats(struct ice_pf *pf);
  * ice_get_tx_pending - returns number of Tx descriptors not processed
  * @ring: the ring of descriptors
  */
-static u32 ice_get_tx_pending(struct ice_ring *ring)
+static u16 ice_get_tx_pending(struct ice_ring *ring)
 {
-	u32 head, tail;
+	u16 head, tail;
 
 	head = ring->next_to_clean;
-	tail = readl(ring->tail);
+	tail = ring->next_to_use;
 
 	if (head != tail)
 		return (head < tail) ?