net: macb: drop `entry` local variable in macb_tx_map()

net: macb: drop `entry` local variable in macb_tx_map()

The pattern:
   entry = macb_tx_ring_wrap(bp, i);
   tx_skb = &queue->tx_skb[entry];
is the exact definition of:
   macb_tx_skb(queue, i);

The pattern:
   entry = macb_tx_ring_wrap(bp, i);
   desc = macb_tx_desc(queue, entry);
is redundant because macb_tx_desc() calls macb_tx_ring_wrap().

One explicit call to macb_tx_ring_wrap() is still required for checking
if it is the last buffer (TX_WRAP case).

Signed-off-by: Théo Lebrun <theo.lebrun@bootlin.com>
Link: https://patch.msgid.link/20251014-macb-cleanup-v1-12-31cd266e22cd@bootlin.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>