[lldb][nfc] Remove no-op calls to Fix*Address (#159586)
The first call, in InitializeNonZerothFrame, is inside a logging branch.
For that, it's better to log the real value instead of the fixed one.
The second call, inside RegisterContextUnwind::ReadFrameAddress, is
computing an address which is then passed to
ReadRegisterValueFromMemory, which boils down to a Process::ReadMemory,
which fixes the address if it wants to. The current variable names are
misleading, making readers believe it is the cfa value itself that is
being passed to Fix*Address; that's not the case. This commit renames
the variable to make this abundantly clear.
