audio/AVRCP: Fix sending invalid response to GetCapabilities
audio/AVRCP: Fix sending invalid response to GetCapabilities

The attribute count has to be initialized with 0 since we reuse the same
buffer for both command and responses it may be already be set causing
invalid response to be generated.

pstglia/external-bluetooth-bluez,pstglia/external-bluetooth-bluez,ComputeCycles/bluez,ComputeCycles/bluez,silent-snowman/bluez,pkarasev3/bluez,pstglia/external-bluetooth-bluez,mapfau/bluez,ComputeCycles/bluez,ComputeCycles/bluez,pstglia/external-bluetooth-bluez,mapfau/bluez,mapfau/bluez,pkarasev3/bluez,pkarasev3/bluez,silent-snowman/bluez,pkarasev3/bluez,silent-snowman/bluez,mapfau/bluez,silent-snowman/bluez