DMA: sudmac: fix compiler warning

Fix the following compiler warning:

drivers/dma/sh/sudmac.c: In function 'sudmac_chan_remove':
drivers/dma/sh/sudmac.c:302: warning: unused variable 'sc'

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski+renesas@gmail.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>