rivafb: fixed reversed DDC ports

Fixed reversed DDC port so assignments are congruent with nvidiafb's and X's
nv driver.

Signed-off-by: Antonino Daplas <adaplas@pol.net>
Cc: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>