Fix flexible array declaration

Author: jepler

devices/ble_hci/common-hal/_bleio/att.c

@@ -61,7 +61,7 @@ STATIC struct {
 typedef struct __packed {
     uint8_t properties;
     uint16_t value_handle;
-    uint8_t uuid[0];  // 2 or 16 bytes
+    uint8_t uuid[];  // 2 or 16 bytes
 } characteristic_declaration_t;
 
 STATIC uint8_t bleio_properties_to_ble_spec_properties(uint8_t bleio_properties) {