soundwire: stream: remove unnecessary variable initializations

A number of variables don't need to be initialized.

In a couple of cases where we loop on a list of runtimes, the code
handling of the 'bus' variable leads to warnings that it may not be
initialized. Add a specific error case to trap such cases.

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20190806005522.22642-10-pierre-louis.bossart@linux.intel.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>