Input: synaptics - fix regression with "image sensor" trackpads

commit 7968a5dd
Input: synaptics - add support for Relative mode

Accidentally broke support for advanced gestures (multitouch)
on some trackpads such as the one in my ThinkPad X220 by
incorretly changing the condition for enabling them. This
restores it.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
CC: stable@kernel.org [3.3]
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>