Input: xpad - don't depend on endpoint order

Input: xpad - don't depend on endpoint order

commit c01b5e7464f0cf20936d7467c7528163c4e2782d upstream.

The order of endpoints is well defined on official Xbox pads, but
we have found at least one 3rd-party pad that doesn't follow the
standard ("Titanfall 2 Xbox One controller" 0e6f:0165).

Fortunately, we get lucky with this specific pad because it uses
endpoint addresses that differ only by direction. We know that
there are other pads out where this is not true, so let's go
ahead and fix this.

Signed-off-by: Cameron Gutman <aicommander@gmail.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
[bwh: Backported to 3.2:
 - Use 'fail3' label in case of failure
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>