Input: atmel_mxt_ts - disable interrupt for 50ms after reset

The CHG/interrupt line is momentarily set (approximately 100 ms) as an
input after power-up or reset for diagnostic purposes. This may cause
spurious interrupts, so disable interrupt handler during this period.

Signed-off-by: Nick Dyer <nick.dyer@itdev.co.uk>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>