dmaengine: idxd: add missing dsa driver unregister

The idxd_unregister_driver() has never been called for the idxd driver upon
removal. Add fix to call unregister driver on module removal.

Fixes: c52ca478

 ("dmaengine: idxd: add configuration component of driver")
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/161947994449.1053102.13189942817915448216.stgit@djiang5-desk3.ch.intel.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>