staging: bcm2835-codec: Pass driver context to create entities

Pass the bcm2835_codec_driver driver context directly into the
bcm2835_codec_create() so that it can be used to store driver global
state. Pass the struct platform_device *pdev by adding it to the driver
global state.

Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>