[media] em28xx: clean up resources should init fail

This patch ensures that the em28xx_init_dev() function cleans up after itself,
in the event that it fails. This isimportant because the struct em28xx will be
deallocated if em28xx_init_dev() returns an error.

[mchehab@redhat.com: Fix merge conflicts and simplify the goto labels]
Signed-off-by: Chris Rankin <rankincj@yahoo.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>