net: enetc: set next_to_clean/next_to_use just from enetc_setup_txbdr()

enetc_alloc_txbdr() deals with allocating resources necessary for a TX
ring to work (the array of software BDs and the array of TSO headers).

The next_to_clean and next_to_use pointers are overwritten with proper
values which are read from hardware here:

enetc_open
-> enetc_alloc_tx_resources
   -> enetc_alloc_txbdr
      -> set to zero
-> enetc_setup_bdrs
   -> enetc_setup_txbdr
      -> read from hardware

So their initialization with zeroes is pointless and confusing.
Delete it.

Consequently, since enetc_setup_txbdr() has no opposite cleanup
function, also delete the resetting of these indices from
enetc_free_tx_ring().

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/freescale/enetc/enetc.c

@@ -1753,9 +1753,6 @@ static int enetc_alloc_txbdr(struct enetc_bdr *txr)
 		goto err_alloc_tso;
 	}
 
-	txr->next_to_clean = 0;
-	txr->next_to_use = 0;
-
 	return 0;
 
 err_alloc_tso:
@@ -1897,9 +1894,6 @@ static void enetc_free_tx_ring(struct enetc_bdr *tx_ring)
 
 		enetc_free_tx_frame(tx_ring, tx_swbd);
 	}
-
-	tx_ring->next_to_clean = 0;
-	tx_ring->next_to_use = 0;
 }
 
 static void enetc_free_rx_ring(struct enetc_bdr *rx_ring)