rtc: make rtc_does_wakealarm() return boolean

Users of rtc_does_wakealarm() return value treat it as boolean so let's
change the signature accordingly.

Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Reviewed-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>