qt: fix postgresql plugin configure

Add upstream patch (see [1], [2]) which fixes a bug introduced by previous
patch '0007-configure-add-psql_config-option.patch'.

[1] https://bugreports.qt.io/browse/QTBUG-45463
[2] https://codereview.qt-project.org/110041



Signed-off-by: Peter Seiderer <ps.report@gmx.net>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>