can: rcar_can: TFCR bitfield conversion

Convert CAN Transmit FIFO Control Register field accesses to use the
FIELD_GET() bitfield access macro.

This gets rid of an explicit shift.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://patch.msgid.link/a8b1dc6f1249a01af9b691ca59e2e5cc2dba6d44.1755857536.git.geert+renesas@glider.be
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

Author: geertu

drivers/net/can/rcar/rcar_can.c

@@ -145,8 +145,6 @@ static const struct can_bittiming_const rcar_can_bittiming_const = {
 /* Transmit FIFO Control Register bits */
 #define RCAR_CAN_TFCR_TFUST	GENMASK(3, 1)	/* Transmit FIFO Unsent Message */
 						/* Number Status Bits */
-#define RCAR_CAN_TFCR_TFUST_SHIFT 1		/* Offset of Transmit FIFO Unsent */
-						/* Message Number Status Bits */
 #define RCAR_CAN_TFCR_TFE	BIT(0)		/* Transmit FIFO Enable */
 
 #define RCAR_CAN_N_RX_MKREGS1	2		/* Number of mask registers */
@@ -377,10 +375,9 @@ static void rcar_can_tx_done(struct net_device *ndev)
 	u8 isr;
 
 	while (1) {
-		u8 unsent = readb(&priv->regs->tfcr);
+		u8 unsent = FIELD_GET(RCAR_CAN_TFCR_TFUST,
+			    readb(&priv->regs->tfcr));
 
-		unsent = (unsent & RCAR_CAN_TFCR_TFUST) >>
-			  RCAR_CAN_TFCR_TFUST_SHIFT;
 		if (priv->tx_head - priv->tx_tail <= unsent)
 			break;
 		stats->tx_packets++;