[clang][analyzer][NFC] Replace dyn_cast with cast in MemRegion::getMemorySpace

[gribozavr]

Summary

MemRegion::getMemorySpace() is annotated with
LLVM_ATTRIBUTE_RETURNS_NONNULL (which triggers instant UB if a null
pointer is returned), and callers indeed don't check the return value
for null. Thus, even though llvm::dyn_cast is called, it can never
return null in this context. Therefore, we can safely call llvm::cast.

[steakhal]

Correct.

clang/lib/StaticAnalyzer/Core/MemRegion.cpp

const MemSpaceRegion *MemRegion::getMemorySpace() const {
   const MemRegion *R = this;
   const auto *SR = dyn_cast<SubRegion>(this);
 
   while (SR) {
     R = SR->getSuperRegion();
     SR = dyn_cast<SubRegion>(R);
   }
 
-  return dyn_cast<MemSpaceRegion>(R);
+  return cast<MemSpaceRegion>(R);
 }
 
 bool MemRegion::hasStackStorage() const {
   return isa<StackSpaceRegion>(getMemorySpace());
 }
 
 bool MemRegion::hasStackNonParametersStorage() const {
   return isa<StackLocalsSpaceRegion>(getMemorySpace());