checkkconfigsymbols.py: support git's "^" syntax

Support git's "^" syntax for diffing two commits, for instance via
"--diff HEAD^^^..HEAD".

Signed-off-by: Michael Ellermann <[email protected]>
Signed-off-by: Valentin Rothberg <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
1 file changed