Input: synaptics - fix crash in synaptics_module_init()

'struct dmi_system_id' arrays must always have a terminator to keep
dmi_check_system() from looking at data (and possibly crashing) it
isn't supposed to look at.

The issue went unnoticed until ef8313bb,
but was introduced about a year earlier with
7705d548 (which also similarly changed
lifebook.c, but the problem there got eliminated shortly afterwards).

The first hunk therefore is a stable candidate back to 2.6.33, while
the full change is needed only on 2.6.38.

Signed-off-by: Jan Beulich <jbeulich@novell.com>
Cc: stable@kernel.org
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>