package/python-cryptography: add host-python3-six host dependency

This dependency wasn't added during the removal of
python3-cryptography.

The conversion/dropping of python3-cryptography was done with commits
[1] and [2], and the commit log of [1] states the dropping of the
host-python3-six dependency was intentionally:

        [...]
        While at it, drop host-python3-pip and host-python3-six as these
        dependencies are not needed. Indeed, pip was never a dependency of
        cryptography and six is not a dependency with python3 and will be
        dropped in version 3.4 and
        https://github.com/pyca/cryptography/commit/e66db8079d3fbd0110e87ece1fd48f4bfd9e48b9
        [...]

But the package python-cryptography is still at version 3.3.2 (and
clearly depends on six)

[1] https://git.buildroot.net/buildroot/commit/?id=95a63a34ac9204c4fe069154783bd97ed48c3ae2
[2] https://git.buildroot.net/buildroot/commit/?id=43147827a7b759248288fad1d97130c027c23e9a

Fixes:
 - http://autobuild.buildroot.net/results/971/9711ccebb9c3e2fa8f17d969d8b431d4301677e3/build-end.log

Reviewed-by: Peter Seiderer <ps.report@gmx.net>
Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/python-cryptography/python-cryptography.mk

@@ -14,7 +14,10 @@ PYTHON_CRYPTOGRAPHY_CPE_ID_VENDOR = cryptography_project
 PYTHON_CRYPTOGRAPHY_CPE_ID_PRODUCT = cryptography
 PYTHON_CRYPTOGRAPHY_DEPENDENCIES = host-python-cffi openssl
 HOST_PYTHON_CRYPTOGRAPHY_NEEDS_HOST_PYTHON = python3
-HOST_PYTHON_CRYPTOGRAPHY_DEPENDENCIES = host-python3-cffi host-openssl
+HOST_PYTHON_CRYPTOGRAPHY_DEPENDENCIES = \
+	host-python3-cffi \
+	host-python3-six \
+	host-openssl
 
 $(eval $(python-package))
 $(eval $(host-python-package))