Input: mousedev - fix regression of inverting axes

Introduced by 987a6c02

 a swap in max/min
calculation gets fixed by this patch.

Reported-by: Bruno Prémont <bonbons@linux-vserver.org>
Signed-off-by: Christoph Fritz <chf.fritz@googlemail.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>