[SYCL][NFC] Fix static code analysis concerns (#2822)

Found via a static-analysis tool:

Inside VisitTemplateTemplateArgument()

    TemplateDecl *TD = TA.getAsTemplate().getAsTemplateDecl(); --->Pointer 'TD' returned from call to function 'getAsTemplateDecl' may be NULL

    TemplateParameterList *TemplateParams = TD->getTemplateParameters(); --> will be dereferenced here

This patch fixes null pointer dereference issues in SemaSYCL.cpp file by adding assert().

Signed-off-by: Soumi Manna <[email protected]>

Author: smanna12

clang/lib/Sema/SemaSYCL.cpp

@@ -3013,6 +3013,7 @@ class SYCLKernelNameTypeVisitor
 
   void VisitTemplateTemplateArgument(const TemplateArgument &TA) {
     TemplateDecl *TD = TA.getAsTemplate().getAsTemplateDecl();
+    assert(TD && "template declaration must be available");
     TemplateParameterList *TemplateParams = TD->getTemplateParameters();
     for (NamedDecl *P : *TemplateParams) {
       if (NonTypeTemplateParmDecl *TemplateParam =
@@ -3594,6 +3595,7 @@ class SYCLFwdDeclEmitter
     // template class Foo specialized by class Baz<Bar>, not a template
     // class template <template <typename> class> class T as it should.
     TemplateDecl *TD = TA.getAsTemplate().getAsTemplateDecl();
+    assert(TD && "template declaration must be available");
     TemplateParameterList *TemplateParams = TD->getTemplateParameters();
     for (NamedDecl *P : *TemplateParams) {
       // If template template parameter type has an enum value template