greybus: bundle: fix gb_bundle_destroy()

Currently gb_bundle_destroy() takes an interface as an argument,
and really doesn't do what a function by that name should do.

What it now does is delete all bundles associated with a given
interface.  What it should do is destroy a single bundle.

Move the looping logic out of gb_bundle_destroy() and into its
caller, gb_interface_destroy().  Pass each bundle in an interface to
gb_bundle_destroy(), which will do what's required to destroy a
single bundle (including removing it from its interface's bundle
list under protection of the lock).

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>