HID: hid-magicmouse: Magic Trackpad has 1 button, not 2

hid-magicmouse was advertising the Apple Magic Trackpad as having 2
buttons (left and right) when it actually only has 1 button.

Advertising multiple buttons makes Xorg disable all button 2 and 3
emulation (using multi-finger clicks). So Xorg users don't get working
right/middle-click emulation out of the box.

This patch makes hid-magicmouse correctly only report one real button
for Magic Trackpad, which in turn makes Xorg enable multi-finger click
support to emulate right/middle buttons.

[http://launchpad.net/bugs/862094]

Signed-off-by: Daniel van Vugt <vanvugt@gmail.com>
Reviewed-by: Chase Douglas <chase.douglas@canonical.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>