commit 8a9af4fd upstream.

usb_ifnum_to_if() can return NULL if the USB device does not have a
configuration installed (usb_device->actconfig == NULL), or if we can't
find the interface number in the installed configuration.  Return an
error instead of crashing.
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>