[Polly] Use LocationSize::unknown() (NFC)

Avoid MemoryLocation::UnknownSize when we're initializing a
LocationSize.

GitOrigin-RevId: eb995e93321622fff99d4fac7ec32d5efd14b337
diff --git a/lib/Analysis/ScopDetection.cpp b/lib/Analysis/ScopDetection.cpp
index 53d0b70..21380c0 100644
--- a/lib/Analysis/ScopDetection.cpp
+++ b/lib/Analysis/ScopDetection.cpp
@@ -1129,7 +1129,7 @@
   AAMDNodes AATags;
   Inst->getAAMetadata(AATags);
   AliasSet &AS = Context.AST.getAliasSetFor(
-      MemoryLocation(BP->getValue(), MemoryLocation::UnknownSize, AATags));
+      MemoryLocation(BP->getValue(), LocationSize::unknown(), AATags));
 
   if (!AS.isMustAlias()) {
     if (PollyUseRuntimeAliasChecks) {