ptp: Add a upper bound on max_vclocks

ptp: Add a upper bound on max_vclocks

syzbot reported WARNING in max_vclocks_store.

This occurs when the argument max is too large for kcalloc to handle.

Extend the guard to guard against values that are too large for
kcalloc

Reported-by: syzbot+94d20db923b9f51be0df@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=94d20db923b9f51be0df
Tested-by: syzbot+94d20db923b9f51be0df@syzkaller.appspotmail.com
Fixes: 73f37068d540 ("ptp: support ptp physical/virtual clocks conversion")
Signed-off-by: I Viswanath <viswanathiyyappan@gmail.com>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Link: https://patch.msgid.link/20250925155908.5034-1-viswanathiyyappan@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>