dmaengine: idxd: fix mapping of portal size

dmaengine: idxd: fix mapping of portal size

Portal size is 4k. Current code is mapping all 4 portals in a single chunk.
Restrict the mapped portal size to a single portal to ensure that submission
only goes to the intended portal address.

Fixes: c52ca478233c ("dmaengine: idxd: add configuration component of driver")
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/160513342642.510187.16450549281618747065.stgit@djiang5-desk3.ch.intel.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>