[media] omap3isp: Clarify the clk_pol field in platform data

The field is used to select the polarity of the pixel clock signal.
"Inverted" and "non inverted" are bad descriptions, specify instead on
which clock edge the signals are sampled.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Sakari Ailus <sakari.ailus@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>