staging: vt6655: return early if not bNeedAck

This patch will check for bNeedAck before making bb_get_frame_time call, so
in case we dont need uAckTime, we can return early.

Signed-off-by: Matej Dujava <mdujava@kocurkovo.cz>
Link: https://lore.kernel.org/r/1588520570-14388-2-git-send-email-mdujava@kocurkovo.cz


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