/dgrp: Fixed warning by adding fallthrough comment

This patch solves the warning "possible switch case/default not preceded
by break or fallthrough comment" for the file
/drivers/staging/dgrp/dgrp_tty.c

Signed-off-by: Andreea-Cristina Bernat <bernat.ada@gmail.com>
Signed-off-by: Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@intel.com>
diff --git a/drivers/staging/dgrp/dgrp_tty.c b/drivers/staging/dgrp/dgrp_tty.c
index 7a9694c..9dba943 100644
--- a/drivers/staging/dgrp/dgrp_tty.c
+++ b/drivers/staging/dgrp/dgrp_tty.c
@@ -2798,6 +2798,7 @@
 		}
 
 		/* pretend we didn't recognize this */
+		/* fall-through */
 
 	case DIGI_SETA:
 		return dgrp_tty_digiseta(tty, (struct digi_struct *) arg);