RDP: fix library path

The library path is here
   /usr/lib/x86_64-linux-gnu/qt5/plugins/krdc/kcms/
Without the patch, it searchs
   /usr/lib/x86_64-linux-gnu/qt5/plugins/
And it'll fail to open rdp settings from system settings dialog.

Signed-off-by: AceLan Kao <acelan@acelan.idv.tw>