fix ledger: nano s did not work reliably since last fw update

follow LedgerHQ/btchip-python@6e985b558f22d1fc0367f5c1730822750337cf94

plugins/ledger/ledger.py

@@ -523,8 +523,15 @@ class LedgerPlugin(HW_PluginBase):
 
     def get_btchip_device(self, device):
         ledger = False
-        if (device.product_key[0] == 0x2581 and device.product_key[1] == 0x3b7c) or (device.product_key[0] == 0x2581 and device.product_key[1] == 0x4b7c) or (device.product_key[0] == 0x2c97):
-           ledger = True
+        if device.product_key[0] == 0x2581 and device.product_key[1] == 0x3b7c:
+            ledger = True
+        if device.product_key[0] == 0x2581 and device.product_key[1] == 0x4b7c:
+            ledger = True
+        if device.product_key[0] == 0x2c97:
+            if device.interface_number == 0 or device.usage_page == 0xffa0:
+                ledger = True
+            else:
+                return None  # non-compatible interface of a nano s or blue
         dev = hid.device()
         dev.open_path(device.path)
         dev.set_nonblocking(True)