[SYCL][NFC] Fix Static Analyzer bugs

[smanna12]

This patch fixes two possible null pointer dereferences issues:

1. In CodeGenModule::Release(): Dereferencing a pointer that might be
   nullptr RD->getAttr() when calling getAspectsMD().

2. In Sema::ActOnFinishFunctionBody(): Passing null pointer FD to
   hasAttr, which dereferences it.

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

[smanna12]

Thank you @premanandrao for reviews!

[smanna12]

@intel/llvm-gatekeepers , This PR is ready to merge. Thank you