chalk: add missing include in a .ui

This fixes FTBFS on a system with minimal-ish configuration of
tqt/tdelibs.

Signed-off-by: Alexander Golubev <fatzer2@gmail.com>

chalk/ui/wdgautogradient.ui

@@ -394,6 +394,7 @@
 </images>
 <layoutdefaults spacing="6" margin="11"/>
 <includes>
+    <include location="global" impldecl="in implementation">knuminput.h</include>
     <include location="global" impldecl="in implementation">kcolorbutton.h</include>
 </includes>
 </UI>