net: fddi: skfp: Mark expected switch fall-through

In preparation to enabling -Wimplicit-fallthrough, mark switch
cases where we are expecting to fall through.

Warning level 3 was used: -Wimplicit-fallthrough=3

This patch is part of the ongoing efforts to enabling
-Wimplicit-fallthrough.
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/fddi/skfp/pcmplc.c

@@ -851,6 +851,7 @@ static void pcm_fsm(struct s_smc *smc, struct s_phy *phy, int cmd)
 
 	case ACTIONS(PC5_SIGNAL) :
 		ACTIONS_DONE() ;
+		/* fall through */
 	case PC5_SIGNAL :
 		if ((cmd != PC_SIGNAL) && (cmd != PC_TIMEOUT_LCT))
 			break ;