Fixed wrong name for the first argument in class methods.
Pylint complains about the issue this way:
Class method should have 'cls' as first argument
(From OE-Core rev: cd7c72d6d5a5110173d0d3f60f2991b1dc30fc26)
Signed-off-by: Ed Bartosh <ed.bartosh@linux.intel.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>