audio: Make 'surroundSound' element optional

This element makes sense only for TV platforms. The deserializer
treats it as optional. Update the schema to match this.

Bug: 116356348
Test: xmllint --noout --xinclude --schema \
      hardware/interfaces/audio/5.0/config/audio_policy_configuration.xsd \
      frameworks/av/services/audiopolicy/config/audio_policy_configuration.xml

Change-Id: I822c3ff10a6becc859d3d44fd58ef2ebcd3d40b1
diff --git a/audio/5.0/config/audio_policy_configuration.xsd b/audio/5.0/config/audio_policy_configuration.xsd
index ee3a437..c580b25 100644
--- a/audio/5.0/config/audio_policy_configuration.xsd
+++ b/audio/5.0/config/audio_policy_configuration.xsd
@@ -42,7 +42,7 @@
                 <xs:element name="globalConfiguration" type="globalConfiguration"/>
                 <xs:element name="modules" type="modules" maxOccurs="unbounded"/>
                 <xs:element name="volumes" type="volumes" maxOccurs="unbounded"/>
-                <xs:element name="surroundSound" type="surroundSound" />
+                <xs:element name="surroundSound" type="surroundSound" minOccurs="0" />
             </xs:sequence>
             <xs:attribute name="version" type="version"/>
         </xs:complexType>