settings: remove focusable state from home preferences

The current title/summary layout of the home preference declared itself as focusable. This
prevent to the radio button layout to get user tap events over the title/summary. Remove the focusable
attribute since the title/summary layout doesn't need it.

Change-Id: I3980463c6dffdafcdaaf36d4838ee5fd3fdff881
Signed-off-by: Jorge Ruesga <jorge@ruesga.com>