ANDROID: dm: fix signature verification flag

The bug was that the signature verification was only
happening when verity was disabled. It should always
happen when verity is enabled.

Signed-off-by: Badhri Jagan Sridharan <Badhri@google.com>
Change-Id: I2d9354e240d36ea06fc68c2d18d8e87b823a4c2f