MRF: fix MSVC warning about 'truncation of constant value'
MRF: fix MSVC warning about 'truncation of constant value'

Found during GDAL testing:

https://github.com/OSGeo/gdal/commit/a8ce1386ffd363aaef5f60b084280695481f99b0

nasa-gibs/mrf,nasa-gibs/mrf,nasa-gibs/mrf