[ModuloSchedule] Trivial fix for instruction with more than one destination in modulo peeler.

When moving an instruction into a block where it was referenced by a phi when peeling,
refer to the phi's register number and assert that the instruction has it in its destinations.
This way, it also covers instructions with more than one destination.

Patch by Hendrik Greving!

Differential Revision: https://reviews.llvm.org/D80027