[mips][msa] lowerMSABitClear() should use SelectionDAG::getNOT() instead of using a long-winded equivalent.

Now that getConstant(-1, MVT::v2i64) works correctly on MIPS32 we can use
SelectionDAG::getNOT() to produce the bitmask.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194819 91177308-0d34-0410-b5e6-96231b3b80d8