fsconfig: fix pylint warning

Fix pylint warning:
W:292,47: Cell variable lineno defined in loop (cell-var-from-loop)

For the closure function that prints the error message, we actually
want the value of modified lineno within the closure.

Test: run unit tests

Change-Id: I7d08184563d347c826ca1af7558fb8e378f151e1
Signed-off-by: William Roberts <william.c.roberts@intel.com>

tools/fs_config/fs_config_generator.py

@@ -289,6 +289,7 @@ class AIDHeaderParser(object):
 
             def error_message(msg):
                 """Creates an error message with the current parsing state."""
+                # pylint: disable=cell-var-from-loop
                 return 'Error "{}" in file: "{}" on line: {}'.format(
                     msg, self._aid_header, str(lineno))