Different calculation for latent heat upper limit for ground water

[ccarouge]

In the latent heat code, we calculate an upper limit using:

CABLE/src/science/canopy/cbl_latent_heat.F90

Line 214 in 630e2e1

fupper_limit(j) = REAL(ssnow_wb(j)-ssnow_wbice(j)/frozen_limit)*frescale(j)

Because the ground water uses a different calculation for wb, we need to introduce a specific case for the gw_model modifying the upper line to:

     fupper_limit(j) = REAL(ssnow_wb(j)-ssnow_wbice(j)*den_rat/frozen_limit)*frescale(j)

Note: the difference in the calculation of wb and wbliq in the ground water is in question, so this issue should be paused while the question is investigated.