package/python-mako: add missing dependency on python-markupsafe

Mako imports markupsafe so it needs to be selected when selecting
BR2_PACKAGE_PYTHON_MAKO.

Fixes:

  https://bugs.busybox.net/show_bug.cgi?id=15628

Signed-off-by: Sebastian Weyer <sebastian.weyer@smile.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>