tty: gdm724x: 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 constants to UL to keep min() and avoid min_t().

Signed-off-by: "Jiri Slaby (SUSE)" <jirislaby@kernel.org>
Cc: linux-staging@lists.linux.dev
Link: https://lore.kernel.org/r/20230810091510.13006-35-jirislaby@kernel.org


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