Fix BT audio examples (#472)

When audio is initialised twice we get a error and make it more obvious
how to change the pins for audio hat hardware

Author: peterharperuk

pico_w/bt/btstack_audio_pico.c

@@ -153,8 +153,9 @@ static int btstack_audio_pico_sink_init(
 
     playback_callback  = playback;
 
-    btstack_audio_pico_audio_buffer_pool = init_audio(samplerate, channels);
-
+    if (!btstack_audio_pico_audio_buffer_pool) {
+        btstack_audio_pico_audio_buffer_pool = init_audio(samplerate, channels);
+    }
     return 0;
 }
 

pico_w/bt/hfp_hf_demo/CMakeLists.txt

@@ -1 +1,6 @@
-picow_bt_example(hfp_hf_demo pico_btstack_sco_demo_util pico_btstack_sbc_encoder)
+add_library(hfp_hf_demo_pins INTERFACE)
+target_compile_definitions(hfp_hf_demo_pins INTERFACE
+    PICO_AUDIO_I2S_DATA_PIN=9
+    PICO_AUDIO_I2S_CLOCK_PIN_BASE=10
+    )
+picow_bt_example(hfp_hf_demo pico_btstack_sco_demo_util pico_btstack_sbc_encoder hfp_hf_demo_pins)

pico_w/bt/mod_player/CMakeLists.txt

@@ -1 +1,6 @@
-picow_bt_example(mod_player pico_btstack_hxcmod_player)
+add_library(mod_player_pins INTERFACE)
+target_compile_definitions(mod_player_pins INTERFACE
+    PICO_AUDIO_I2S_DATA_PIN=9
+    PICO_AUDIO_I2S_CLOCK_PIN_BASE=10
+    )
+picow_bt_example(mod_player pico_btstack_hxcmod_player mod_player_pins)

pico_w/bt/sine_player/CMakeLists.txt

@@ -1 +1,6 @@
-picow_bt_example(sine_player)
+add_library(sine_player_pins INTERFACE)
+target_compile_definitions(sine_player_pins INTERFACE
+    PICO_AUDIO_I2S_DATA_PIN=9
+    PICO_AUDIO_I2S_CLOCK_PIN_BASE=10
+    )
+picow_bt_example(sine_player sine_player_pins)