dmaengine: idxd: add engine 'struct device' missing bus type assignment

engine 'struct device' setup is missing assigning the bus type. Add it to
dsa_bus_type.

Fixes: 75b91130

 ("dmaengine: idxd: fix engine conf_dev lifetime")
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/161947841562.984844.17505646725993659651.stgit@djiang5-desk3.ch.intel.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>