tty: tty_buffer: Add a blank line after declarations

Add a blank line after declarations, reported by checkpatch.pl.

Signed-off-by: Xiaofei Tan <tanxiaofei@huawei.com>
Link: https://lore.kernel.org/r/1620811585-18582-4-git-send-email-tanxiaofei@huawei.com


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