[test] Fix const-str-array-decay.cl failure on PowerPC

D150520 converted the test to use opaque pointers. The update version
fails on PowerPC because of different return type of the function.
This patch resolves the failure by removing the return type check;
it also makes the test look more like it was before the conversion to
prevent other potential issues caused by ABI differences across targets.

clang/test/CodeGenOpenCL/const-str-array-decay.cl

@@ -6,4 +6,5 @@ kernel void str_array_decy() {
   test_func("Test string literal");
 }
 
-// CHECK: call i32 @test_func(ptr addrspace(2) noundef @{{.*}})
+// CHECK: ptr addrspace(2) noundef
+// CHECK-NOT: addrspacecast