Bluetooth: CAP: Mark err used for assert as __maybe_unused

If asserts are disabled, then `err` is unused can caused
a compiler warning.

Signed-off-by: Emil Gydesen <[email protected]>

Author: Thalley

subsys/bluetooth/audio/cap_handover.c

@@ -23,6 +23,7 @@
 #include <zephyr/logging/log.h>
 #include <zephyr/sys/__assert.h>
 #include <zephyr/sys/util.h>
+#include <zephyr/toolchain.h>
 
 #include "bap_endpoint.h"
 #include "cap_internal.h"
@@ -146,7 +147,7 @@ void bt_cap_handover_broadcast_source_stopped(uint8_t reason)
 	if (proc_param->is_unicast_to_broadcast) {
 		LOG_DBG("Unexpected broadcast source stop with reason 0x%02x", reason);
 
-		const int err = bt_cap_initiator_broadcast_audio_delete(
+		__maybe_unused const int err = bt_cap_initiator_broadcast_audio_delete(
 			proc_param->unicast_to_broadcast.broadcast_source);
 
 		__ASSERT_NO_MSG(err == 0);