media: imon: Fix null-ptr-deref in imon_probe

It seems that the return value of usb_ifnum_to_if() can be NULL and
needs to be checked.

Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Tested-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
diff --git a/drivers/media/rc/imon.c b/drivers/media/rc/imon.c
index 9724fe8..9fef8cc 100644
--- a/drivers/media/rc/imon.c
+++ b/drivers/media/rc/imon.c
@@ -2515,6 +2515,11 @@
 	mutex_lock(&driver_lock);
 
 	first_if = usb_ifnum_to_if(usbdev, 0);
+	if (!first_if) {
+		ret = -ENODEV;
+		goto fail;
+	}
+
 	first_if_ctx = usb_get_intfdata(first_if);
 
 	if (ifnum == 0) {