b43: Use fallthrough pseudo-keyword

Replace the existing /* fall through */ comments and its variants with
the new pseudo-keyword macro fallthrough[1].

[1] https://www.kernel.org/doc/html/v5.7/process/deprecated.html?highlight=fallthrough#implicit-switch-case-fall-through

Signed-off-by: Gustavo A. R. Silva <[e-mail]>
Signed-off-by: Kalle Valo <[e-mail]>
Link: https://lore.kernel.org/r/20200821064218.GA19502@embeddedor

drivers/net/wireless/broadcom/b43/dma.c

···
 		switch (queue_prio) {
 		default:
 			B43_WARN_ON(1);
-			/* fallthrough */
+			fallthrough;
 		case 0:
 			ring = dev->dma.tx_ring_AC_VO;
 			break;

drivers/net/wireless/broadcom/b43/main.c

···
 	switch (reason) {
 	default:
 		b43dbg(dev->wl, "The panic reason is unknown.\n");
-		/* fallthrough */
+		fallthrough;
 	case B43_FWPANIC_DIE:
 		/* Do not restart the controller or firmware.
 		 * The device is nonfunctional from now on.
···
 		size = be32_to_cpu(hdr->size);
 		if (size != ctx->blob->size - sizeof(struct b43_fw_header))
 			goto err_format;
-		/* fallthrough */
+		fallthrough;
 	case B43_FW_TYPE_IV:
 		if (hdr->ver != 1)
 			goto err_format;
···
 		b43_rate_memory_write(dev, B43_OFDM_RATE_36MB, 1);
 		b43_rate_memory_write(dev, B43_OFDM_RATE_48MB, 1);
 		b43_rate_memory_write(dev, B43_OFDM_RATE_54MB, 1);
-		/* fallthrough */
+		fallthrough;
 	case B43_PHYTYPE_B:
 		b43_rate_memory_write(dev, B43_CCK_RATE_1MB, 0);
 		b43_rate_memory_write(dev, B43_CCK_RATE_2MB, 0);
···
 		/* There are 14e4:4321 PCI devs with 2.4 GHz BCM4321 (N-PHY) */
 		if (dev->phy.type != B43_PHYTYPE_G)
 			break;
-		/* fall through */
+		fallthrough;
 	case 0x4313: /* BCM4311 */
 	case 0x431a: /* BCM4318 */
 	case 0x432a: /* BCM4321 */

drivers/net/wireless/broadcom/b43/phy_n.c

···
 		if (!(dev->phy.rev >= 4 &&
 		      b43_current_band(dev->wl) == NL80211_BAND_2GHZ))
 			break;
-		/* FALL THROUGH */
+		fallthrough;
 	case 0:
 	case 1:
 		b43_ntab_write_bulk(dev, B43_NTAB16(8, 0x08), 4, vmid);

drivers/net/wireless/broadcom/b43/pio.c

···
 		switch (queue_prio) {
 		default:
 			B43_WARN_ON(1);
-			/* fallthrough */
+			fallthrough;
 		case 0:
 			q = dev->pio.tx_queue_AC_VO;
 			break;

drivers/net/wireless/broadcom/b43/tables_nphy.c

···
 		case 5:
 			if (sprom->fem.ghz2.extpa_gain == 3)
 				return b43_ntab_tx_gain_epa_rev3_hi_pwr_2g;
-			/* fall through */
+			fallthrough;
 		case 4:
 		case 3:
 			return b43_ntab_tx_gain_epa_rev3_2g;