[media] em28xx: unregister i2c bus 0 if bus 1 fails to register

Fix the error handling logic, making it to unregister i2c bus 0, in
case of a failure to register the second bus.

Reported-by: Frank Schäfer <fschaefer.oss@googlemail.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>