Input: pixcir_i2c_ts - simplify input device initialization

input_mt_init_slots() will perform necessary settings for performing
multi-touch to single-touch emulation, we do not need to do that ourselves.

Acked-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>