Cleanup convert_SI_unit and misc linter warnings

Change-Id: I000ba548b79a7023aabad653125842064fa2e7cb
Signed-off-by: Galantsev, Dmitrii <dmitrii.galantsev@amd.com>

py-interface/amdsmi_exception.py

@@ -107,6 +107,7 @@ class AmdSmiTimeoutException(AmdSmiLibraryException):
 class AmdSmiParameterException(AmdSmiException):
     def __init__(self, receivedValue, expectedType, msg=None):
         super().__init__(msg)
+        self.err_code = None
         self.actualType = type(receivedValue)
         self.expectedType = expectedType
         self.set_err_msg()