livepatch/sample: Use the right type for the leaking data pointer

The "leak" pointer, in the sample of shadow variable API, is allocated
as sizeof(int). Let's help developers and static analyzers with
understanding the code by using the appropriate pointer type.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
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>