staging: android-alarm: Fix bad index when canceling alarms[]

It was using ANDROID_ALARM_ELAPSED_REALTIME_WAKEUP_MASK as an
index.

CC: Arve Hjønnevåg <arve@android.com>
CC: Android Kernel Team <kernel-team@android.com>
CC: JP Abgrall <jpa@google.com>
Change-Id: I919860cc71254453e382616bce9fd5455802cb3d
Signed-off-by: JP Abgrall <jpa@google.com>
[jstultz: Tweaked commit subject]
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>