dma: sh/shdma-base.c: remove unnecessary null pointer check

the variable chan is dereferenced in line 635, so it is no reason to check
null again in line 641.
Signed-off-by: Cong Ding <dinggnu@gmail.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

drivers/dma/sh/shdma-base.c

@@ -638,9 +638,6 @@ static int shdma_control(struct dma_chan *chan, enum dma_ctrl_cmd cmd,
 	unsigned long flags;
 	int ret;
 
-	if (!chan)
-		return -EINVAL;
-
 	switch (cmd) {
 	case DMA_TERMINATE_ALL:
 		spin_lock_irqsave(&schan->chan_lock, flags);