Correct diffusion coefficients for tke in LES (#2034)

Correct diffusion coefficients for tke in LES (#2034)

TYPE: bug-fix

KEYWORDS: Diffusion of tke

SOURCE: internal (issue raised by Branko Kosovic)

DESCRIPTION OF CHANGES:
Problem:
Reported in #2026 For km_opt=2, tke diffusion should be twice momentum diffusion, but was twice heat diffusion (three times larger). For km_opt=5 it was 3 times momentum diffusion instead of twice.

Solution:
xkmv and xkmh passed into diffusion routines for tke calls instead of xkhv and xkhh.

ISSUE: For use when this PR closes an issue.
Fixes #2026

LIST OF MODIFIED FILES:
modified:   dyn_em/module_diffusion_em.F

TESTS CONDUCTED:
1. LES case was run with shalconv sounding to verify the change.
2. The Jenkins tests are all passing.

RELEASE NOTE: km_opt=2 and km_opt=5 tke diffusion was reduced to one third its value to match theory.