staging: dgnc: Need to check for NULL of ch

the "ch" from brd structure could be NULL, it need to
check for NULL.

Signed-off-by: Daeseok Youn <daeseok.youn@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/dgnc/dgnc_neo.c

@@ -380,7 +380,7 @@ static inline void neo_parse_isr(struct dgnc_board *brd, uint port)
 	unsigned long flags;
 
 	ch = brd->channels[port];
-	if (ch->magic != DGNC_CHANNEL_MAGIC)
+	if (!ch || ch->magic != DGNC_CHANNEL_MAGIC)
 		return;
 
 	/* Here we try to figure out what caused the interrupt to happen */