Fix the usage issue of getRegMask.

[wdx727]

In the process of determining whether two MachineOperands are equal and calculating the hash of a MachineOperand, both MO_RegisterMask and MO_RegisterLiveOut types were uniformly handled. However, when the type is MO_RegisterLiveOut, calling getRegMask() triggers an assertion failure. This PR addresses this issue.

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[wdx727]

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[wdx727]

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