mml_dust coordinate isn't actually set

[ekluzek]

The dust bins should be defined in the mml_dust coordinate in histFileMod.F90. This is defined, but the values are NOT set. We haven't noticed this before for some reason, but I noticed it in the cesm2_3_slim branch PR for this test...

PEM_Vmct.f19_f19_mg17.I1850SlimRsGs.cheyenne_intel.slim-default COMPARE_base_modpes

mml_dust was different between the two PE layouts. One was garbage data and the other had it sent to missing value. So we just need to set the bin sizes with the actual sizes.

[ekluzek]

I've got this mostly working in #49, although so far I'm just setting it to missing_value. I need to figure out the actual dust bin ranges and have it set to the actual values. But, at least the tests work correctly with it set to missing value.