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

drivers/dma/idxd/idxd.h

@@ -370,7 +370,6 @@ static inline void idxd_dev_set_type(struct idxd_dev *idev, int type)
 }
 
 extern struct bus_type dsa_bus_type;
-extern struct bus_type iax_bus_type;
 
 extern bool support_enqcmd;
 extern struct ida idxd_ida;