libdvr: add interface that dvb get demux source. [2/2]

PD#SWPL-30408

Problem:
DVB all channel display black mute after exit VMX-WEB video.

Solution:
Add interface that dvb_get_demux_source.
Reset demux source before acquire demux res.

Verify:
u215.

Signed-off-by: Chuanzhi Wang <chuanzhi.wang@amlogic.com>
Change-Id: I253e20b8582414e84a01a738703303afd821a0c4
diff --git a/include/dvb_utils.h b/include/dvb_utils.h
index 3df3fae..b339ebe 100644
--- a/include/dvb_utils.h
+++ b/include/dvb_utils.h
@@ -27,6 +27,16 @@
  */
 int dvb_set_demux_source (int dmx_idx, DVB_DemuxSource_t src);
 
+/**
+ * Get the demux's input source.
+ * \param dmx_idx Demux device's index.
+ * \param point src that demux's input source.
+ * \retval 0 On success.
+ * \retval -1 On error.
+ */
+int dvb_get_demux_source (int dmx_idx, DVB_DemuxSource_t *src);
+
+
 #ifdef __cplusplus
 }
 #endif