dmaengine: dw-edma: Fix Using plain integer as NULL pointer in dw-edma-v0-debugfs.c

Fixes warning given by executing "make C=2 drivers/dma/dw-edma/"

Sparse output:
drivers/dma/dw-edma/dw-edma-v0-debugfs.c:296:49: warning:
Using plain integer as NULL pointer

Cc: Joao Pinto <[e-mail]>
Signed-off-by: Gustavo Pimentel <[e-mail]>
Link: https://lore.kernel.org/r/6569fd8c[e-mail]
Signed-off-by: Vinod Koul <[e-mail]>

drivers/dma/dw-edma/dw-edma-v0-debugfs.c

···
 	if (!regs)
 		return;
 
-	base_dir = debugfs_create_dir(dw->name, 0);
+	base_dir = debugfs_create_dir(dw->name, NULL);
 	if (!base_dir)
 		return;