[Clang][NFC] Avoid duplication in BuildDeductionGuideForTypeAlias (llvm#161948)

This addresses the post-commit review llvm#161035 (comment) from Shafik

Author: zyn0217

clang/lib/Sema/SemaTemplateDeductionGuide.cpp

@@ -1189,27 +1189,20 @@ BuildDeductionGuideForTypeAlias(Sema &SemaRef,
     // parameter list of a synthesized CTAD guide. See also the FIXME in
     // test/SemaCXX/cxx20-ctad-type-alias.cpp:test25.
     Sema::CheckTemplateArgumentInfo CTAI;
+    for (auto TA : Output.arguments())
+      if (SemaRef.CheckTemplateArgument(
+              TP, TA, F, F->getLocation(), F->getLocation(),
+              /*ArgumentPackIndex=*/-1, CTAI,
+              Sema::CheckTemplateArgumentKind::CTAK_Specified))
+        return nullptr;
     if (Input.getArgument().getKind() == TemplateArgument::Pack) {
-      for (auto TA : Output.arguments()) {
-        if (SemaRef.CheckTemplateArgument(
-                TP, TA, F, F->getLocation(), F->getLocation(),
-                /*ArgumentPackIndex=*/-1, CTAI,
-                Sema::CheckTemplateArgumentKind::CTAK_Specified))
-          return nullptr;
-      }
       // We will substitute the non-deduced template arguments with these
       // transformed (unpacked at this point) arguments, where that substitution
       // requires a pack for the corresponding parameter packs.
       TemplateArgsForBuildingFPrime[Index] =
           TemplateArgument::CreatePackCopy(Context, CTAI.SugaredConverted);
     } else {
       assert(Output.arguments().size() == 1);
-      TemplateArgumentLoc Transformed = Output.arguments()[0];
-      if (SemaRef.CheckTemplateArgument(
-              TP, Transformed, F, F->getLocation(), F->getLocation(),
-              /*ArgumentPackIndex=*/-1, CTAI,
-              Sema::CheckTemplateArgumentKind::CTAK_Specified))
-        return nullptr;
       TemplateArgsForBuildingFPrime[Index] = CTAI.SugaredConverted[0];
     }
   }