n_tty: Convert no_space_left to space_left boolean

The no_space_left variable is only assigned with 0 and 1.

Change its type to boolean and move negation from its name into the
check.

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20230309082035.14880-2-ilpo.jarvinen@linux.intel.com


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