Input: atmel_mxt_ts - use mxt_acquire_irq in mxt_soft_reset

If using IRQF_TRIGGER_FALLING, then there is a race here: if the reset
completes before we enable the IRQ, then CHG is already low and touch
will be broken.

This has been seen on Chromebook Pixel 2.

A workaround is to reconfig T18 COMMSCONFIG to enable the RETRIGEN bit
using mxt-app:
    mxt-app -W -T18 44
    mxt-app --backup

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