s390/vmcp: simplify vmcp_response_free()

Get rid of the goto and "out" label within vmcp_response_free() which
I added. This just makes the code harder to read than necessary.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>