[analyzer] [NFC] Simplify SVal::getAsLocSymbol function using existing functions

[ASDenysPetrov]

Summary

Method of obtaining MemRegion from LocAsInteger/MemRegionVal already exists in SVal::getAsRegion function. Replace repetitive conditions in SVal::getAsLocSymbol with SVal::getAsRegion function.

[NoQ]

Looks correct, thanks!

clang/lib/StaticAnalyzer/Core/SVals.cpp

 /// return that SymbolRef.  Otherwise return 0.
 ///
 /// Implicit casts (ex: void* -> char*) can turn Symbolic region into Element
 /// region. If that is the case, gets the underlining region.
 /// When IncludeBaseRegions is set to true and the SubRegion is non-symbolic,
 /// the first symbolic parent region is returned.
 SymbolRef SVal::getAsLocSymbol(bool IncludeBaseRegions) const {
   // FIXME: should we consider SymbolRef wrapped in CodeTextRegion?
-  if (Optional<nonloc::LocAsInteger> X = getAs<nonloc::LocAsInteger>())
-    return X->getLoc().getAsLocSymbol(IncludeBaseRegions);
-
-  if (Optional<loc::MemRegionVal> X = getAs<loc::MemRegionVal>()) {
-    const MemRegion *R = X->getRegion();
-    if (const SymbolicRegion *SymR = IncludeBaseRegions ?
-                                      R->getSymbolicBase() :
-                                      dyn_cast<SymbolicRegion>(R->StripCasts()))
+  if (const MemRegion *R = getAsRegion())
+    if (const SymbolicRegion *SymR =
+            IncludeBaseRegions ? R->getSymbolicBase()
+                               : dyn_cast<SymbolicRegion>(R->StripCasts()))
       return SymR->getSymbol();
-  }
+
   return nullptr;
 }
 
 /// Get the symbol in the SVal or its base region.
 SymbolRef SVal::getLocSymbolInBase() const {
   Optional<loc::MemRegionVal> X = getAs<loc::MemRegionVal>();
 
   if (!X)