futex: Handle invalid node numbers supplied by user

syzbot used a negative node number which was not rejected early and led
to invalid memory access in node_possible().

Reject negative node numbers except for FUTEX_NO_NODE.

[bigeasy: Keep the FUTEX_NO_NODE check]

Closes: https://lore.kernel.org/all/6835bfe3.a70a0220.253bc2.00b5.GAE@google.com/


Fixes: cec199c5 ("futex: Implement FUTEX2_NUMA")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reported-by:  <syzbot+9afaf6749e3a7aa1bdf3@syzkaller.appspotmail.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20250528085521.1938355-4-bigeasy@linutronix.de