Fix AttributeError for "sfputil show error-status -hw" (sonic-net#291)

When insert trasnceiver which is not QSFP-DD, "sfputil show error-status -hw" would fail
error:
  File "/usr/local/lib/python3.7/dist-packages/sonic_platform_base/sonic_xcvr/sfp_optoe_base.py", line 211, in get_error_description
    return api.get_error_description() if api is not None else None
AttributeError: 'Sff8636Api' object has no attribute 'get_error_description'

Signed-off-by: chiourung_huang <[email protected]>

Author: chiourung

sonic_platform_base/sonic_xcvr/api/xcvr_api.py

@@ -463,3 +463,15 @@ def get_module_fw_info(self):
         result                     |tuple          |firmware information
         """
         raise NotImplementedError
+
+    def get_error_description(self):
+        """
+        Retrives the error descriptions of the SFP module
+
+        Returns:
+            String that represents the current error descriptions of vendor specific errors
+            In case there are multiple errors, they should be joined by '|',
+            like: "Bad EEPROM|Unsupported cable"
+        """
+        raise NotImplementedError
+