There is no point in having a generic broadcast function if it needs to
have special cases for each callback it broadcasts.

Abstract the error broadcast to only the necessary information and removes
the now unnecessary helper to walk the bus.
Signed-off-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Sinan Kaya <okaya@kernel.org>