[NUI] Fix Build warnings: GetFunctionPointerFor

[NUI] Fix Build warnings: GetFunctionPointerFor

warning CS0618: 'Marshal.GetFunctionPointerForDelegate(Delegate)' is obsolete:
'GetFunctionPointerForDelegate(Delegate) may be unavailable in future releases.
Instead, use GetFunctionPointerForDelegate<T>(T).
For more info, go to http://go.microsoft.com/fwlink/?LinkID=296522 '

Change-Id: I35855172e65cb489245baf94537d61d694cfed0b
Signed-off-by: huiyu,eun <huiyu.eun@samsung.com>