[RISCV] When custom iseling masked stores, copy the mask into V0 instead of virtual...

[RISCV] When custom iseling masked stores, copy the mask into V0 instead of virtual register.

I missed a few intrinsics in 3dd4aa7d09599507d1f801ffe4bec4c9eebbb8da
when I did this for masked loads and masked segment loads/stores.

Found while trying to share more code between these custom isel
functions.