Revert r238200: "[MIPS] fix extension of integer types (function calls)"

mips-unsigned-ext-var.c and mips-unsigned-extend.c fail in some builds.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@238237 91177308-0d34-0410-b5e6-96231b3b80d8