NimBLE: Update submodule to fix bug in delete bond procedure

- Fixes bug in `get_nvs_db_attribute` related to getting correct index while
  deleting bond in NVS.
- MR raised on esp-nimble branch: https://gitlab.espressif.cn:6688/espressif/esp-nimble/merge_requests/12

components/bt/host/nimble/nimble

@@ -1 +1 @@
-Subproject commit 30480fdb5d11547bba8c34647dbfc629c6fdb74c
+Subproject commit 7600a6f60308c77fec755a024d51ab2fb7d11553