Release the EGL context after initialization.

Threaded applications like qmlscene could not bind the EGL context if
the context is already bound in the other thread.

Change-Id: Ia75ef9e76ebff48aa2c9b348101ab2f388e18c5e
Reviewed-by: Andy Nichols <andy.nichols@nokia.com>

src/plugins/platforms/kms/qkmsbuffermanager.cpp

@@ -121,6 +121,8 @@ void QKmsBufferManager::setupBuffersForMode(const drmModeModeInfo &mode, int num
                               GL_COLOR_ATTACHMENT0,
                               GL_RENDERBUFFER,
                               this->renderTargetBuffer());
+
+    eglMakeCurrent(m_screen->device()->eglDisplay(), EGL_NO_SURFACE, EGL_NO_SURFACE, EGL_NO_CONTEXT);
 }
 
 void QKmsBufferManager::clearBuffers()