staging: vt6655: Update function description

The function vt6655_get_current_tsf has been updated while its
description has not. Update the description to correctly reflect
what it does.

Signed-off-by: Nam Cao <namcaov@gmail.com>
Link: https://lore.kernel.org/r/20220529160211.GA5805@nam-dell


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