[ELF] Simplify with dyn_cast_or_null. NFC

llvm-svn: 367126
diff --git a/lld/ELF/Symbols.cpp b/lld/ELF/Symbols.cpp
index 2267730..a9bc613 100644
--- a/lld/ELF/Symbols.cpp
+++ b/lld/ELF/Symbols.cpp
@@ -560,7 +560,7 @@
   auto *oldSym = cast<Defined>(this);
   auto *newSym = cast<Defined>(other);
 
-  if (other->file && isa<BitcodeFile>(other->file))
+  if (dyn_cast_or_null<BitcodeFile>(other->file))
     return 0;
 
   if (!oldSym->section && !newSym->section && oldSym->value == newSym->value &&