Fix possible panic caused by unlocked access to tty->read_cnt in
while-loop condition in n_tty_read().
Signed-off-by: NStanislav Kozina <skozina@redhat.com>
Signed-off-by: NAlan Cox <alan@linux.intel.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>