net: dp83640: Mark expected switch fall-throughs

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

Notice that in this particular case, I replaced the code comment at the
top of the switch statement with a proper "fall through" annotation for
each case, which is what GCC is expecting to find.

Addresses-Coverity-ID: 1056542 ("Missing break in switch")
Addresses-Coverity-ID: 1339579 ("Missing break in switch")
Addresses-Coverity-ID: 1369526 ("Missing break in switch")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/dp83640.c

@@ -757,13 +757,16 @@ static int decode_evnt(struct dp83640_private *dp83640,
 
 	phy_txts = data;
 
-	switch (words) { /* fall through in every case */
+	switch (words) {
 	case 3:
 		dp83640->edata.sec_hi = phy_txts->sec_hi;
+		/* fall through */
 	case 2:
 		dp83640->edata.sec_lo = phy_txts->sec_lo;
+		/* fall through */
 	case 1:
 		dp83640->edata.ns_hi = phy_txts->ns_hi;
+		/* fall through */
 	case 0:
 		dp83640->edata.ns_lo = phy_txts->ns_lo;
 	}