Fix Qt5 migration of HostArmQtKeyFilter

Change the contant value of power key to prevent a compile error when enabling USE_KEY_FILTER

Open-webOS-DCO-1.0-Signed-off-by: Kwangsub Kim <kwangsub.kim@palm.com>

Change-Id: I2e0ca9dafc3a3952ac0140c13360c4761be34469