Input: ad7877 - convert to using timer_setup()

In preparation for unconditionally passing the struct timer_list pointer to
all timer callbacks, switch to using the new timer_setup() and from_timer()
to pass the timer pointer explicitly.

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