Fix height of "add blocked number" button on the blocked numbers screen.

The text view was set to use a fixed layout height; changing to
wrap_content ensures with larger font sizes that the label is not cut off.

Fixes: 203232774
Test: Flash device with build; change display --> font size to max.  Load
the Dialer --> Settings --> Blocked Numbers screen.  Add a blocked number.
Verify that the "Add" link is not cut off.

Change-Id: Ib36eaf532d79c504de571b63f8db83ca769f8eca