tty: vcc: convert counts to size_t

Unify the type of tty_operations::write() counters with the 'count'
parameter. I.e. use size_t for them.

This includes changing vcc_port::chars_in_buffer to size_t to keep min()
and avoid min_t().

Signed-off-by: "Jiri Slaby (SUSE)" <jirislaby@kernel.org>
Cc: "David S. Miller" <davem@davemloft.net>
Link: https://lore.kernel.org/r/20230810091510.13006-34-jirislaby@kernel.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>