[media] DVB, DiB9000: Fix leak in dib9000_attach()

If the second memory allocation in dib9000_attach() fails, we'll leak the
memory allocated by the first.

Signed-off-by: Jesper Juhl <jj@chaosbits.net>
Cc: Patrick Boettcher <patrick.boettcher@dibcom.fr>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>