soundwire: call startup function for remaining slave init

Slave devices attached to the WCD soundwire master would perform
device enumeration to determine the devices connected on the bus.
To perform this enumeration, call soundwire startup function to
invoke slave device startup function.

Change-Id: I96a21d9fe14b4bb0d8324dafcd8f4bfd63aa559e
Signed-off-by: Banajit Goswami <bgoswami@codeaurora.org>