dbus: Fix the Seek method's introspection data

The position is an input parameter, not a return value.
Signed-off-by: Mirsal Ennaime <mirsal@videolan.org>
(cherry picked from commit d77c14f0)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/control/dbus/dbus_introspect.h

@@ -88,7 +88,7 @@ static const char* psz_introspection_xml =
 "    <method name=\"Pause\" />\n"
 "    <method name=\"PlayPause\" />\n"
 "    <method name=\"Seek\">\n"
-"      <arg type=\"x\" direction=\"out\" />\n"
+"      <arg type=\"x\" direction=\"in\" />\n"
 "    </method>"
 "    <method name=\"OpenUri\">\n"
 "      <arg type=\"s\" direction=\"in\" />\n"