selftests/memfd/memfd_test: fix possible NULL pointer dereference

If `name' is NULL, a NULL pointer may be accessed in printf.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: liuye <[e-mail]>
Reviewed-by: Lorenzo Stoakes <[e-mail]>
Cc: Greg Thelen <[e-mail]>
Cc: "Isaac J. Manjarres" <[e-mail]>
Cc: Jeff Xu <[e-mail]>
Cc: Saurav Shah <[e-mail]>
Cc: Shuah Khan (Samsung OSG) <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

tools/testing/selftests/memfd/memfd_test.c

···
 	r = sys_memfd_create(name, flags);
 	if (r >= 0) {
 		printf("memfd_create(\"%s\", %u) succeeded, but failure expected\n",
-		       name, flags);
+		       name ? name : "NULL", flags);
 		close(r);
 		abort();
 	}