media: dvb-usb: fix uninit-value in dvb_usb_adapter_dvb_init

If dibusb_read_eeprom_byte fails, the mac address is not initialized.
And nova_t_read_mac_address does not handle this failure, which leads to
the uninit-value in dvb_usb_adapter_dvb_init.

Fix this by handling the failure of dibusb_read_eeprom_byte.

Reported-by:  <syzbot+e27b4fd589762b0b9329@syzkaller.appspotmail.com>
Fixes: 786baecf ("[media] dvb-usb: move it to drivers/media/usb/dvb-usb")
Signed-off-by: Dongliang Mu <mudongliangabcd@gmail.com>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

drivers/media/usb/dvb-usb/nova-t-usb2.c

@@ -130,7 +130,7 @@ static int nova_t_rc_query(struct dvb_usb_device *d, u32 *event, int *state)
 
 static int nova_t_read_mac_address (struct dvb_usb_device *d, u8 mac[6])
 {
-	int i;
+	int i, ret;
 	u8 b;
 
 	mac[0] = 0x00;
@@ -139,7 +139,9 @@ static int nova_t_read_mac_address (struct dvb_usb_device *d, u8 mac[6])
 
 	/* this is a complete guess, but works for my box */
 	for (i = 136; i < 139; i++) {
-		dibusb_read_eeprom_byte(d,i, &b);
+		ret = dibusb_read_eeprom_byte(d, i, &b);
+		if (ret)
+			return ret;
 
 		mac[5 - (i - 136)] = b;
 	}