[mips][msa] A small refactor to reduce patch noise in my next commit

No functional change. An if-statement has been split into two nested if-statements.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@195972 91177308-0d34-0410-b5e6-96231b3b80d8
[mips][msa] MSA loads and stores have a 10-bit offset. Account for this when lowering FrameIndex.

This prevents the compiler from emitting invalid ld.[bhwd]'s and st.[bhwd]'s
when the stack frame is between 512 and 32,768 bytes in size.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@195973 91177308-0d34-0410-b5e6-96231b3b80d8