Overwrite destination link if it already exists.

The original install rule would fail if the link already existed.
Now installing succeeds if the destination was already there, it will
be overwritten with the new file.

src/Makefile.am

@@ -75,7 +75,7 @@ noinst_HEADERS = $(source_h)
 install-data-hook:
 	cd $(DESTDIR)$(LIBVA_DRIVERS_PATH) ;			\
 	for drv in $(DRIVERS); do				\
-	    ln -s xvba_drv_video.so $${drv}_drv_video.so;	\
+	    ln -sf xvba_drv_video.so $${drv}_drv_video.so;	\
 	done
 
 # Extra clean files so that maintainer-clean removes *everything*