[RISCV] Fix double counting CSRs with Zcmp in RISCVFrameLowering::getFrameIndexReference. (#117207)
The Zcmp callee saved registers are already accounted for in
getCalleeSavedStackSize(). Subtracting RVPushStackSize subtracts
them a second time leading to incorrect stack offsets during frame
index elimination.
This should have been removed in
0de2b26942f890a6ec84cd75ac7abe3f6f2b2e37
when Zcmp handling was changed. Prior to that, RVPushStackSize was
not included in getCalleeSavedStackSize(). The commit message at the
time noted that Zcmp+RVV was likely broken.