usb: musb: musb_cppi41: Dont reprogram DMA if tear down is initiated

Reprogramming the DMA after tear down is initiated leads to warning.
This is mainly seen with ISOCH since we do a delayed completion for
ISOCH transfers. In ISOCH transfers dma_completion should not reprogram
if the channel tear down is initiated.

Signed-off-by: George Cherian <george.cherian@ti.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>