device connection: Remove struct device_connection

Since the connection descriptors can't be stored into the
list anymore, there is no need for the data structure.

Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Link: https://lore.kernel.org/r/20200904125123.83725-4-heikki.krogerus@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>