net: plip: fix break; causing plip to never transmit

Since commit
71ae2cb30531 ("net: plip: Fix fall-through warnings for Clang")

plip was not able to send any packets, this patch replaces one
unintended break; with fallthrough; which was originally missed by
commit 9525d69a3667 ("net: plip: mark expected switch fall-throughs").

I have verified with a real hardware PLIP connection that everything
works once again after applying this patch.

Fixes: 71ae2cb30531 ("net: plip: Fix fall-through warnings for Clang")
Signed-off-by: Jakub Boehm <[e-mail]>
Reviewed-by: Simon Horman <[e-mail]>
Message-ID: <[e-mail]>
Signed-off-by: Andrew Lunn <[e-mail]>

drivers/net/plip/plip.c

···
 				return HS_TIMEOUT;
 			}
 		}
-		break;
+		fallthrough;
 
 	case PLIP_PK_LENGTH_LSB:
 		if (plip_send(nibble_timeout, dev,