Input: da9063 - fix capability and drop KEY_SLEEP

Since commit f889beaa ("Input: da9063 - report KEY_POWER instead of
KEY_SLEEP during power key-press") KEY_SLEEP isn't supported anymore. This
caused input device to not generate any events if "dlg,disable-key-power"
is set.

Fix this by unconditionally setting KEY_POWER capability, and not
declaring KEY_SLEEP.

Fixes: f889beaa

 ("Input: da9063 - report KEY_POWER instead of KEY_SLEEP during power key-press")
Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
Cc: stable@vger.kernel.org
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>