libsass: fix fetched commit hash

libsass: fix fetched commit hash

Old commit hash is for v3.6.5, not v3.6.6.
https://github.com/sass/libsass/tags
Old version contains several vulnerabilities.

Note that exact recipe copy of recipe introduced in oe-core was never
present in oe.

Signed-off-by: Peter Marko <peter.marko@siemens.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>