dmaengine: ti-dma-crossbar: Fix possible race condition with dma_inuse

When looking for unused xbar_out lane we should also protect the set_bit()
call with the same mutex to protect against concurrent threads picking the
same ID.

Fixes: ec9bfa1e ("dmaengine: ti-dma-crossbar: dra7: Use bitops instead of idr")
Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Cc: stable@vger.kernel.org
Signed-off-by: Vinod Koul <vinod.koul@intel.com>