fixed grad reg for SCAN functionals, calculate p directly (#146)
fixed grad reg for SCAN functionals, calculate p directly (#146)

Co-authored-by: James Furness <d565fb9351ca57b841f7e782330c0013c607de89@nottingham.ac.uk>
robertodr/xcfun,dftlibs/xcfun,dftlibs/xcfun,robertodr/xcfun,robertodr/xcfun,robertodr/xcfun,dftlibs/xcfun,dftlibs/xcfun