[media] V4L: mt9m111: fix pixel clock

This camera driver supports only rising edge, which is the default
setting of the device. The function mt9m111_setup_pixfmt() overwrites
this setting. So the driver actually uses falling edge.
This patch corrects that.

Signed-off-by: Teresa Gámez <t.gamez@phytec.de>
[g.liakhovetski@gmx.de: removed superfluous register write]
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Tested-by: Teresa Gámez <t.gamez@phytec.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>