viafb: correct sync polarity for OLPC DCON

While the OLPC display appears to be able to handle either positive
or negative sync, the Display Controller only recognises positive sync.

This brings viafb (for XO-1.5) in line with lxfb (for XO-1) and
fixes a recent regression where the XO-1.5 DCON could no longer be
frozen. Thanks to Florian Tobias Schandinat for helping identify
the fix.

Test case: from a vt,
	echo 1 > /sys/devices/platform/dcon/freeze
should cause the current screen contents to freeze, rather than garbage being
displayed.
Signed-off-by: NDaniel Drake <dsd@laptop.org>
Signed-off-by: NFlorian Tobias Schandinat <FlorianSchandinat@gmx.de>
Cc: stable@kernel.org

drivers/video/via/share.h

@@ -559,8 +559,8 @@
 #define M1200X720_R60_VSP       POSITIVE
 
 /* 1200x900@60 Sync Polarity (DCON) */
-#define M1200X900_R60_HSP       NEGATIVE
-#define M1200X900_R60_VSP       NEGATIVE
+#define M1200X900_R60_HSP       POSITIVE
+#define M1200X900_R60_VSP       POSITIVE
 
 /* 1280x600@60 Sync Polarity (GTF Mode) */
 #define M1280x600_R60_HSP       NEGATIVE