treewide: Use fallthrough pseudo-keyword

Replace the existing /* fall through */ comments and its variants with
the new pseudo-keyword macro fallthrough[1]. Also, remove unnecessary
fall-through markings when it is the case.

[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 <gustavoars@kernel.org>

drivers/net/ethernet/sun/cassini.c

@@ -4759,7 +4759,7 @@ static int cas_ioctl(struct net_device *dev, struct ifreq *ifr, int cmd)
 	switch (cmd) {
 	case SIOCGMIIPHY:		/* Get address of MII PHY in use. */
 		data->phy_id = cp->phy_addr;
-		/* Fallthrough... */
+		fallthrough;
 
 	case SIOCGMIIREG:		/* Read MII PHY register. */
 		spin_lock_irqsave(&cp->lock, flags);

drivers/net/ethernet/sun/niu.c

@@ -8835,7 +8835,7 @@ static int walk_phys(struct niu *np, struct niu_parent *parent)
 			else
 				goto unknown_vg_1g_port;
 
-			/* fallthru */
+			fallthrough;
 		case 0x22:
 			val = (phy_encode(PORT_TYPE_10G, 0) |
 			       phy_encode(PORT_TYPE_10G, 1) |
@@ -8860,7 +8860,7 @@ static int walk_phys(struct niu *np, struct niu_parent *parent)
 			else
 				goto unknown_vg_1g_port;
 
-			/* fallthru */
+			fallthrough;
 		case 0x13:
 			if ((lowest_10g & 0x7) == 0)
 				val = (phy_encode(PORT_TYPE_10G, 0) |

drivers/net/ethernet/sun/sungem.c

@@ -2712,7 +2712,7 @@ static int gem_ioctl(struct net_device *dev, struct ifreq *ifr, int cmd)
 	switch (cmd) {
 	case SIOCGMIIPHY:		/* Get address of MII PHY in use. */
 		data->phy_id = gp->mii_phy_addr;
-		/* Fallthrough... */
+		fallthrough;
 
 	case SIOCGMIIREG:		/* Read MII PHY register. */
 		data->val_out = __sungem_phy_read(gp, data->phy_id & 0x1f,