Fix 'libgomp.oacc-c-c++-common/kernels-decompose-1.c' expected diagnostics

Fix-up for recent commit 8935589b
"OMP lowering: Regimplify 'OMP_CLAUSE_MAP_DECL_MAKE_ADDRESSABLE' DECLs
[PR100280, PR104132, PR104133]": adjust for a GCN offloading workaround
added just before commit: '(volatile void *) &f1;'.

	PR testsuite/104791
	libgomp/
	* testsuite/libgomp.oacc-c-c++-common/kernels-decompose-1.c: Fix
	expected diagnostics.