[RISCV] Use RISCV::RVVBitsPerBlock instead of 64 in getLMUL1VT. NFC#144401

topperc merged 1 commit intollvm:mainllvm/llvm-project:mainfrom

topperc:pr/rvvbitsperblocktopperc/llvm-project:pr/rvvbitsperblockCopy head branch name to clipboard