selftests/futex: Add newline to ksft_exit_fail_msg()

This was missed in commit e5c04d0 ("selftests/futex: Refactor
futex_wait with kselftest_harness.h") while replacing previous perror()
calls, which automatically append the newline character.

Fixes: e5c04d0 ("selftests/futex: Refactor futex_wait with kselftest_harness.h")
Signed-off-by: Carlos Llamas <cmllamas@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://patch.msgid.link/20251015173556.2899646-1-cmllamas@google.com

Author: Carlos Llamas

tools/testing/selftests/futex/functional/futex_wait.c

@@ -108,14 +108,14 @@ TEST(file_backed)
 	/* Testing a file backed shared memory */
 	fd = open(SHM_PATH, O_RDWR | O_CREAT, S_IRUSR | S_IWUSR);
 	if (fd < 0)
-		ksft_exit_fail_msg("open");
+		ksft_exit_fail_msg("open\n");
 
 	if (ftruncate(fd, sizeof(f_private)))
-		ksft_exit_fail_msg("ftruncate");
+		ksft_exit_fail_msg("ftruncate\n");
 
 	shm = mmap(NULL, sizeof(f_private), PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
 	if (shm == MAP_FAILED)
-		ksft_exit_fail_msg("mmap");
+		ksft_exit_fail_msg("mmap\n");
 
 	memcpy(shm, &f_private, sizeof(f_private));