staging: vt6656: CARDqGetNextTBTT replace code using do_div.

uBeaconInterval becomes u32

get next TBTT value using vendor's equation as shown.

This patch was checked against the original code
and yields exactly the same value.

Signed-off-by: Malcolm Priestley <tvboxspy@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>