selinux: Fix fall-through warnings for Clang

In preparation to enable -Wimplicit-fallthrough for Clang, fix a warning
by explicitly adding a break statement instead of letting the code fall
through to the next case.

Link: https://github.com/KSPP/linux/issues/115
Signed-off-by: Gustavo A. R. Silva <[e-mail]>
Signed-off-by: Paul Moore <[e-mail]>

security/selinux/hooks.c

···
 	switch (id) {
 	case LOADING_MODULE:
 		rc = selinux_kernel_module_from_file(NULL);
+		break;
 	default:
 		break;
 	}