python-pyasn: fix version number to match upstream tarball

The upstream tarball at
https://pypi.python.org/packages/source/p/pyasn1/

 is actually in
version 0.1.7, not 0.17.

Reported-by: Peter Korsgaard <jacmet@uclibc.org>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>