use vendor_id instead of cpu_vendor_id in gentoo module

Author: mboisson

modules/gentoo/2020.lua.core

@@ -60,7 +60,7 @@ elseif arch == "avx" then
 else
         setenv("PIP_CONFIG_FILE", "/cvmfs/soft.computecanada.ca/config/python/pip-gentoo.conf")
 end
-setenv("MII_INDEX_FILE", "/cvmfs/soft.computecanada.ca/custom/mii/data/" .. arch .. "_" .. cpu_vendor_id)
+setenv("MII_INDEX_FILE", "/cvmfs/soft.computecanada.ca/custom/mii/data/" .. arch .. "_" .. vendor_id)
 
 -- also make easybuild and easybuild-generated modules accessible
 prepend_path("PATH", "/cvmfs/soft.computecanada.ca/easybuild/bin")