Input: mpr121 - improve sensibility of touch key

The Quick Charge bit in Electrode conf register should be set in init
function. This bit was missed in chip's document, which may cause touch
controller charge too slow to generate an interrupt.

Also, adjust the default vlaue of touch and release threshold
to make touch key more sensitive, this fix touch may not sensitive
after setup with plastic case.

Signed-off-by: Jiejing Zhang <jiejing.zhang@freescale.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>