Fix testcases up after recent -Wreturn-type change

Fix testcases up after recent -Wreturn-type change

I missed these two testcases in the diff when looking for testcases
that fail. The change is the same as what was done for
gcc.dg/Wreturn-mismatch-2.c.

Pushed as obvious after a quick test.

gcc/testsuite/ChangeLog:

	* gcc.dg/Wreturn-mismatch-2a.c: Change dg-warning
	for the last -Wreturn-type to dg-bogus.
	* gcc.dg/Wreturn-mismatch-6.c: Likewise.

Signed-off-by: Andrew Pinski <quic_apinski@quicinc.com>