The PIXDATA flags of the display_flags enum are controller centric,
e.g. NEGEDGE means the controller shall drive the data signals on
pixelclocks negative edge. However, the drivers flag is display
centric: Sample the data on negative (falling) edge.

Therefore, change the if statement to check for the POSEDGE flag
(which is typically not set):
Drive on positive edge => sample on negative edge

Signed-off-by: Stefan Agner <stefan@agner.ch>
Acked-by: Shawn Guo <shawnguo@kernel.org>
Cc: Jean-Christophe Plagniol-Villard <plagnioj@jcrosoft.com>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Cc: Liu Ying <Ying.Liu@freescale.com>
Cc: Lothar Waßmann <LW@KARO-electronics.de>
Cc: Fabio Estevam <fabio.estevam@freescale.com>
Cc: Max Krummenacher <max.krummenacher@toradex.com>
Cc: Mauro Salvini <mauro.salvini@smigroup.net>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>