dmaengine: idxd: add RO check for wq max_batch_size write

dmaengine: idxd: add RO check for wq max_batch_size write

Block wq_max_batch_size_store() when the device is configured as read-only
and not configurable.

Fixes: e7184b159dd3 ("dmaengine: idxd: add support for configurable max wq batch size")
Reported-by: Bernice Zhang <[email protected]>
Tested-by: Bernice Zhang <[email protected]>
Signed-off-by: Dave Jiang <[email protected]>
Link: https://lore.kernel.org/r/164971493551.2201159.1942042593642155209.stgit@djiang5-desk3.ch.intel.com
Signed-off-by: Vinod Koul <[email protected]>