staging: vt6655: do calculation of uAckTime first

This patch is extracting calculation of uAckTime in one place, at the
start of case body.

Signed-off-by: Matej Dujava <mdujava@kocurkovo.cz>
Link: https://lore.kernel.org/r/1588512552-12297-3-git-send-email-mdujava@kocurkovo.cz


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