livepatch: Handle allocation failure in the sample of shadow variable API

klp_shadow_alloc() is not handled in the sample of shadow variable API.
It is not strictly necessary because livepatch_fix1_dummy_free() is
able to handle the potential failure. But it is an example and it should
use the API a clean way.

Signed-off-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Joe Lawrence <joe.lawrence@redhat.com>
Acked-by: Miroslav Benes <mbenes@suse.cz>
Reviewed-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>