Fix keyguard landscape layout on phones

This particular layout didn't have layout_height specified, which
is undefined.  However, the undefined behavior seems to have changed
on the platform to one where this layout no longer works.  Not
specifying layout_height causes the security area view to be 0 pixels
wide, effectively ignoring layout_weight.

Fixes bug 7283261

Change-Id: I0e3d156e9b2d7ef1492dec9791f0e241e8cd7fe6