missing factors in hllc riemann solver (see Toro: (10.38), (10.39))

(cherry picked from commit b3f2463f)

I'm pretty sure there is a factor missing in the expressions for the momentum and energy flux of the HLLC riemann solver (when compared to Toro 2009, eqs. 10.38 and 10.39). It doesn't seem to have a noticeable impact on most hydro tests though...