drm/i2c: tda998x: cleanup from previous changes

Cleanup the code a little from the effects of the previous changes:
- Move tda998x_destroy() to be above tda998x_create()
- Use 'dev' directly in tda998x_create() where appropriate.

Tested-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>