tty: n_tty: use time_is_before_jiffies() in n_tty_receive_overrun()

tty: n_tty: use time_is_before_jiffies() in n_tty_receive_overrun()

The jiffies tests in n_tty_receive_overrun() are simplified ratelimiting
(without locking). We could use struct ratelimit_state and the helpers,
but to me, it occurs to be too complex for this use case.

But the code currently tests both if the time passed (the first
time_after()) and if jiffies wrapped around (the second time_after()).
time_is_before_jiffies() takes care of both, provided overrun_time is
initialized at the allocation time.

So switch to time_is_before_jiffies(), the same what ratelimiting does.

Signed-off-by: "Jiri Slaby (SUSE)" <jirislaby@kernel.org>
Link: https://lore.kernel.org/r/20230827074147.2287-5-jirislaby@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>