wic: Code cleanup: bad-classmethod-argument

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>

scripts/lib/wic/plugins/imager/direct_plugin.py

@@ -36,7 +36,7 @@ class DirectPlugin(ImagerPlugin):
     name = 'direct'
 
     @classmethod
-    def __rootfs_dir_to_dict(self, rootfs_dirs):
+    def __rootfs_dir_to_dict(cls, rootfs_dirs):
         """
         Gets a string that contain 'connection=dir' splitted by
         space and return a dict
@@ -49,7 +49,7 @@ class DirectPlugin(ImagerPlugin):
         return krootfs_dir
 
     @classmethod
-    def do_create(self, subcmd, opts, *args):
+    def do_create(cls, subcmd, opts, *args):
         """
         Create direct image, called from creator as 'direct' cmd
         """
@@ -67,7 +67,7 @@ class DirectPlugin(ImagerPlugin):
         image_output_dir = args[5]
         oe_builddir = args[6]
 
-        krootfs_dir = self.__rootfs_dir_to_dict(rootfs_dir)
+        krootfs_dir = cls.__rootfs_dir_to_dict(rootfs_dir)
 
         configmgr._ksconf = ksconf