tests/ptrace.c: tweak magic constants to make the test more reliable

* tests/ptrace.c (main): Change bad_request and bad_data to make they
lower 32-bit parts closer to -1U.
diff --git a/tests/ptrace.c b/tests/ptrace.c
index c6c74fb..3810bd6 100644
--- a/tests/ptrace.c
+++ b/tests/ptrace.c
@@ -172,9 +172,9 @@
 main(void)
 {
 	const unsigned long bad_request =
-		(unsigned long) 0xdeadbeeffacefeed;
+		(unsigned long) 0xdeadbeeffffffeed;
 	const unsigned long bad_data =
-		(unsigned long) 0xdeadcafefacef00d;
+		(unsigned long) 0xdeadcafefffff00d;
 	const unsigned long pid =
 		(unsigned long) 0xdefaced00000000 | (unsigned) getpid();