sizeof counts the terminating null character as well, so that also
contributed to the ID computed for the X11 atom. But the convention is
for only the non-null characters to contribute to the atom ID.
Fixes: 2e12fe425f "loader/dri3: Enable adaptive_sync via
_VARIABLE_REFRESH property"
Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: Eric Anholt <eric@anholt.net>