checkstyle.py uses single-quoted strings in most locations already.
There are a few locations where this wouldn't be convenient (when the
string itself contains a single quote, which would then require
escaping), but there are also a few other locations where double quotes
are used when single quotes would work fine. Change those to standardize
on single-quoted strings.
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
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