staging: line6: toneport.c: Fix for possible null pointer dereference

The NULL check was done to late, and there it was a risk
of a possible null pointer dereference.

This was partially found by using a static code analysis program called cppcheck.
Signed-off-by: Rickard Strandqvist <rickard_strandqvist@spectrumdigital.se>
Reviewed-by: Stefan Hajnoczi <stefanha@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

drivers/staging/line6/toneport.c

@@ -433,12 +433,16 @@ void line6_toneport_reset_resume(struct usb_line6_toneport *toneport)
 void line6_toneport_disconnect(struct usb_interface *interface)
 {
 	struct usb_line6_toneport *toneport;
+	struct snd_line6_pcm *line6pcm;
 	u16 idProduct;
 
 	if (interface == NULL)
 		return;
 
 	toneport = usb_get_intfdata(interface);
+	if (NULL == toneport)
+		return;
+
 	del_timer_sync(&toneport->timer);
 	idProduct = le16_to_cpu(toneport->line6.usbdev->descriptor.idProduct);
 
@@ -447,14 +451,11 @@ void line6_toneport_disconnect(struct usb_interface *interface)
 		device_remove_file(&interface->dev, &dev_attr_led_green);
 	}
 
-	if (toneport != NULL) {
-		struct snd_line6_pcm *line6pcm = toneport->line6.line6pcm;
-
+	line6pcm = toneport->line6.line6pcm;
 	if (line6pcm != NULL) {
 		line6_pcm_release(line6pcm, LINE6_BITS_PCM_MONITOR);
 		line6_pcm_disconnect(line6pcm);
 	}
-	}
 
 	toneport_destruct(interface);
 }