Merging cases with duplicate attribute values do not work with reqd_work_group_size attribute

[smanna12]

Merging cases do not work with reqd_work_group_size attribute
[[sycl::reqd_work_group_size(64, 64, 64)]] void f();/ expected-note {{conflicting attribute is here}} now OK
[[sycl::reqd_work_group_size(128, 128, 128,)]] void f(); // expected-warning{{attribute 'reqd_work_group_size' is already applied with different parameters}} now OK