ASoC: dapm: fix debugfs read using path->connected

This fix a bug in dapm_widget_power_read_file(),
where it may sent opposite order of source/sink widget
into the p->connected().

for example,
static int connected_check(source, sink);
{"w_sink", NULL, "w_source", connected_check}

the dapm_widget_power_read_file() will query p->connected()
in following case
	p->conneted("w_source", "w_sink")
	p->conneted("w_sink", "w_source")
we should avoid the last case, since it's the wrong order (source/sink)
as declared in snd_soc_dapm_route.

Signed-off-by: KaiChieh Chuang <kaichieh.chuang@mediatek.com>
Signed-off-by: Mark Brown <broonie@kernel.org>