[llvm] [MIPS] Fix -msingle-float doesn't work with double on O32 (PR #107543)

[YunQiang Su via llvm-commits]

wzssyqa wrote:

Ohh. Thanks. Your patch fixes this problem.

And I will approve this PR once you fix the problem Matt found.
I guess he meant that you can just remove `N->getOpcode() == ISD::BITCAST`

https://github.com/llvm/llvm-project/pull/107543