[media] smiapp: Clean up smiapp_get_pdata()

Don't set rval when it's not used (the function returns a pointer to struct
smiapp_platform_data).

Signed-off-by: Sakari Ailus <sakari.ailus@iki.fi>
Acked-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>