glsvgoverlaysink: fix do_get_property

An exception is silently raised when called, typically eaten by
the plugin loader:
GObject.get_property() argument 1 must be str, not gobject.GParamSpec

BUG: 144376463
Change-Id: I0a66bfadb7243eeb5c633692be21427a4b99dad9
diff --git a/plugins/glsvgoverlaysink.py b/plugins/glsvgoverlaysink.py
index 75957df..0b78aa1 100644
--- a/plugins/glsvgoverlaysink.py
+++ b/plugins/glsvgoverlaysink.py
@@ -413,7 +413,7 @@
             self.glimagesink.set_property(prop.name, value)
 
     def do_get_property(self, prop):
-        return self.glimagesink.get_property(prop)
+        return self.glimagesink.get_property(prop.name)
 
     def init_gl(self, glcontext):
         assert not self.shader
@@ -655,4 +655,4 @@
         return gst_context
 
 
-__gstelementfactory__ = ("glsvgoverlaysink", Gst.Rank.NONE, GlSvgOverlaySink)
+__gstelementfactory__ = ('glsvgoverlaysink', Gst.Rank.NONE, GlSvgOverlaySink)