[RISCV] Fix alias printing for vmnot.m

By clearing the HasDummyMask flag from mask register binary operations
and mask load/store.

HasDummyMask was causing an extra operand to get appended when
converting from MachineInstr to MCInst. This extra operand doesn't
appear in the assembly string so was mostly ignored, but it prevented
the alias instruction printing from working correctly.

Reviewed By: arcbbb

Differential Revision: https://reviews.llvm.org/D124424