USB: Remove unneeded pointer intf from speedtch_upload_firmware()

This trivial patch removes the unneeded pointer intf returned from
usb_ifnum_to_if(), which is never used. The check for NULL can be simply done
by if (!usb_ifnum_to_if(usb_dev, 2)).

Signed-off-by: Micah Gruber <micah.gruber@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>