dmaengine: ti-dma-crossbar: Correct am335x/am43xx mux value type

The used 0x1f mask is only valid for am335x family of SoC, different family
using this type of crossbar might have different number of electable
events. In case of am43xx family 0x3f mask should have been used for
example.
Instead of trying to handle each family's mask, just use u8 type to store
the mux value since the event offsets are aligned to byte offset.

Fixes: 42dbdcc6 ("dmaengine: ti-dma-crossbar: Add support for crossbar on AM33xx/AM43xx")
Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>