Input: ads7846 - stop updating dev->power.power_state

This stops the ads7846 driver from using dev->power.power_state; that field is
deprecated (overdue for removal) and the only reason to update it was to make
the /sys/devices/.../power/state files (now removed) work better.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>