nimble/hs: Make ble_eatt_start static and void

It is not used outside of ble_eatt.c
diff --git a/nimble/host/src/ble_eatt.c b/nimble/host/src/ble_eatt.c
index f9f7d92..9fad2a8 100644
--- a/nimble/host/src/ble_eatt.c
+++ b/nimble/host/src/ble_eatt.c
@@ -76,6 +76,7 @@
 static struct ble_npl_event g_read_sup_srv_feat_ev;
 
 static void ble_eatt_setup_cb(struct ble_npl_event *ev);
+static void ble_eatt_start(uint16_t conn_handle);
 
 static struct ble_eatt *
 ble_eatt_find_not_busy(uint16_t conn_handle)
@@ -520,7 +521,7 @@
     return rc;
 }
 
-int
+static void
 ble_eatt_start(uint16_t conn_handle)
 {
     struct ble_gap_conn_desc desc;
@@ -533,21 +534,18 @@
         /* Let master to create ecoc.
          * TODO: Slave could setup after some timeout
          */
-        return 0;
+        return;
     }
 
     eatt = ble_eatt_alloc();
     if (!eatt) {
-        BLE_EATT_LOG_ERROR("eatt: no available eatt resources\n");
-        return 0;
+        return;
     }
 
     eatt->conn_handle = conn_handle;
 
     /* Setup EATT  */
     ble_npl_eventq_put(ble_hs_evq_get(), &eatt->setup_ev);
-
-    return 0;
 }
 
 void
diff --git a/nimble/host/src/ble_eatt_priv.h b/nimble/host/src/ble_eatt_priv.h
index d5d01bd..d3c9877 100644
--- a/nimble/host/src/ble_eatt_priv.h
+++ b/nimble/host/src/ble_eatt_priv.h
@@ -36,7 +36,6 @@
 uint16_t ble_eatt_get_available_chan_cid(uint16_t conn_handle, uint8_t op);
 void ble_eatt_release_chan(uint16_t conn_handle, uint8_t op);
 int ble_eatt_tx(uint16_t conn_handle, uint16_t cid, struct os_mbuf *txom);
-int ble_eatt_start(uint16_t conn_handle);
 #else
 static inline void
 ble_eatt_init(ble_eatt_att_rx_fn att_rx_fn)
@@ -54,11 +53,5 @@
 {
     return BLE_L2CAP_CID_ATT;
 }
-
-static inline int
-ble_eatt_start(uint16_t conn_handle)
-{
-    return 0;
-}
 #endif
 #endif