Fix uninitialized bug in GFDL MP

[mathomp4]

CI tests with Debugging flags on found a bug in GFDL Microphysics. Namely the code has:

    real :: TOT_PREC_LS, AREA_LS_PRC, AREA_LS_PRC_K
    integer :: k

    revap(:) = 0.

    do k = ktop, kbot

        TOT_PREC_LS = TOT_PREC_LS  + (          ( qr (k) + qs (k) + qg (k) ) * den (k) )
        AREA_LS_PRC = AREA_LS_PRC  + ( qa (k) * ( qr (k) + qs (k) + qg (k) ) * den (k) )

The issue is that in the k-loop both TOT_PREC_LS and AREA_LS_PRC are uninitialized in the first run through the loop.

My fix is to initialize to 0.0 before going into the loop. I assume this is right, but I'll defer to @wmputman.

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ETA: My editor cleaned up the whitespace, so the file comparison is not too nice to look out without ignoring whitespace. See:

https://github.com/GEOS-ESM/GEOSgcm_GridComp/pull/1035/files?w=1