dmaengine: idxd: remove iax_bus_type prototype

Remove unused iax_bus_type prototype declaration. Should have been removed
when iax_bus_type was removed.

Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/162637462909.744545.7106049898386277608.stgit@djiang5-desk3.ch.intel.com


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