Fix log text placement.

Commit I4b56db78d13931fdd79580b801260bdfca0e9726 intended to constrain
the log to the lower quarter of the screen, but miscalculated the
respective limit value. Also make sure to display the log starting from
the last line.

Change-Id: I87fb2f311ff312faeca8777559d46c1569f6b95f