[flang][runtime] Fix typo in assign.cpp

Variable name 'y' needs to be used in the declaration of 'yDesc'.

Differential Revision: https://reviews.llvm.org/D144117

flang/runtime/assign.cpp

@@ -128,7 +128,7 @@ static inline bool RangesOverlap(const char *aStart, const char *aEnd,
 static bool MayAlias(const Descriptor &x, const Descriptor &y) {
   const char *xDesc{reinterpret_cast<const char *>(&x)};
   const char *xDescLast{xDesc + x.SizeInBytes()};
-  const char *yDesc{reinterpret_cast<const char *>(&x)};
+  const char *yDesc{reinterpret_cast<const char *>(&y)};
   const char *yDescLast{yDesc + y.SizeInBytes()};
   std::int64_t xLeast, xMost, yLeast, yMost;
   MaximalByteOffsetRange(x, xLeast, xMost);