Input: return correct value when setting up absolute device via uinipt.

uinput_alloc_device() is supposed to return the number of bytes read,
the value is returned to uinput_write() and from there to userspace. If
EV_ABS is set then it returns the value from uinput_validate_absbits()
instead, which is zero when everything is ok instead of the count.

Signed-off-by: Ian Campbell <icampbell@arcom.com>
Acked-by: Aristeu Rozanski <aris@cathedrallabs.org>
Signed-off-by: Vojtech Pavlik <vojtech@suse.cz>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>