video: pxa3xx-gcu: pass around struct device *

Instead of passing around struct platform_device, use struct device.
That saves one level of dereference. Also, call platform devices pdev,
and provide a shortcut for &pdev->dev.

Signed-off-by: Daniel Mack <zonque@gmail.com>
Acked-by: Haojian Zhuang <haojian.zhuang@gmail.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>