Fix incorrect expression in directfb keyboard code

Add missing equal sign to have the result of the OR
stored inside the modifiers variable.

Fixes Coverity CID#89071.

Change-Id: I0ee1a080f5f6757ae7646733aa3bb5cf8c6cdeed
Reviewed-by: Simon Hausmann <simon.hausmann@theqtcompany.com>

src/plugins/platforms/directfb/qdirectfbconvenience.cpp

@@ -217,7 +217,7 @@ Qt::KeyboardModifiers QDirectFbConvenience::keyboardModifiers(DFBInputDeviceModi
         modifiers |= Qt::ControlModifier;
     }
     if (mask & DIMM_META) {
-        modifiers | Qt::MetaModifier;
+        modifiers |= Qt::MetaModifier;
     }
     return modifiers;
 }