[Sched] Skip MemOp with unknown size when clustering

In llvm#83875, we changed the type of `Width` to `LocationSize`. To get
the clsuter bytes, we use `LocationSize::getValue()` to calculate
the value.

But when `Width` is an unknown size `LocationSize`, an assertion
"Getting value from an unknown LocationSize!" will be triggered.

This patch simply skips MemOp with unknown size to fix this issue
and keep the logic the same as before.

This issue was found when implementing software pipieliner for
RISC-V in llvm#117546. The pipeliner may clone some memory operations
with `BeforeOrAfterPointer` size.

Author: wangpc-pp

llvm/lib/CodeGen/MachineScheduler.cpp

@@ -1947,6 +1947,9 @@ void BaseMemOpClusterMutation::collectMemOpRecords(
     LocationSize Width = 0;
     if (TII->getMemOperandsWithOffsetWidth(MI, BaseOps, Offset,
                                            OffsetIsScalable, Width, TRI)) {
+      if (!Width.hasValue())
+        continue;
+
       MemOpRecords.push_back(
           MemOpInfo(&SU, BaseOps, Offset, OffsetIsScalable, Width));