systemd: fix typo in avoid-using-system-auth.patch

systemd: fix typo in avoid-using-system-auth.patch

The patch 0015-systemd-user-avoid-using-system-auth.patch
makes PAM session for systemd-user include common-account file
which doesn't contain any session related lines and that breaks
launching "systemd --user" with the error:

Jul 29 13:03:24 intel-corei7-64 systemd[691]: user@0.service: Failed
at step PAM spawning /lib/systemd/systemd: Operation not permitted

This change fixes the patch by including common-session file
instead.

Signed-off-by: Dmitry Rozhkov <dmitry.rozhkov@linux.intel.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>