Input: synaptics - use guard notation when pausing serio port

Using guard notation makes the code more compact and error handling
more robust by ensuring that serio ports are resumed in all code paths
when control leaves critical section.

Link: https://lore.kernel.org/r/20240905041732.2034348-6-dmitry.torokhov@gmail.com


Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>