greybus: Use valid control pointer while freeing memory

While releasing memory during error path exit, invalid memory pointer
was used for dapm_routes. Use a valid one.

Signed-off-by: Vaibhav Agarwal <vaibhav.agarwal@linaro.org>
Reviewed-by: Mark Greer <mgreer@animalcreek.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>