Mms: Pre-view pops up twice after tapping preview button

The flag of the intent needs to be set to single top.

Change-Id: Ibc0fe202bd500054454b28e7caef915ec41e3bc5
Author: Jianli Zhang <jianli.zhang@borqs.com>
Signed-off-by: Jianli Zhang <jianli.zhang@borqs.com>
Signed-off-by: Frederic Predon <frederic.predon@intel.com>
Signed-off-by:Jeevaka Badrappan <jeevaka.badrappan@intel.com>
Signed-off-by: Shuo Gao <shuo.gao@intel.com>
Signed-off-by: Bruce Beare <bruce.j.beare@intel.com>
Signed-off-by: Jack Ren <jack.ren@intel.com>
Author-tracking-BZ: 8583