Input: gpio_keys_polled - always use gpiod_get_value_cansleep

It does not matter if given GPIO may sleep or not when reading state,
polling is always done in a non-atomic context, so we should always
be able to simply use gpiod_get_value_cansleep().

Also let's note in the logs when we fail to read gpio state.

Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Tested-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>