[media] stv090x: handle allocation failures

kmalloc() can fail so check whether state->internal is NULL.
append_internal() can return NULL on allocation failures so check that.
Also if we hit the error condition later in the function then there is
a memory leak and we need to call remove_dev() to fix it.

Also Oliver Endriss pointed out an additional leak that I missed in the
first version of this patch.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Acked-by: Oliver Endriss <o.endriss@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>