mfd: iqs62x: Do not change clock frequency during ATI

After a reset event, the device automatically triggers ATI at the
default core clock frequency (16 MHz). Soon afterward, the driver
loads firmware which may attempt to lower the frequency.

If this initial ATI cycle is still in progress when the frequency
is changed, however, the device incorrectly reports channels 0, 1
and 2 to be in a state of touch once ATI finally completes.

To solve this problem, wait until ATI is complete before lowering
the frequency. Because this particular ATI cycle occurs following
a reset event, its duration is predictable and a simple delay can
suffice.

Signed-off-by: Jeff LaBundy <jeff@labundy.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>