fsl-viu: adjust for OF based clock lookup

after device tree based clock lookup became available, the VIU driver
need no longer use the previous global "viu_clk" name, but should use
the "ipg" clock name specific to the OF node

Cc: Mauro Carvalho Chehab <[e-mail]>
Cc: [e-mail]
Signed-off-by: Gerhard Sittig <[e-mail]>
Signed-off-by: Anatolij Gustschin <[e-mail]>

drivers/media/platform/fsl-viu.c

···
 	}
 
 	/* enable VIU clock */
-	clk = devm_clk_get(&op->dev, "viu_clk");
+	clk = devm_clk_get(&op->dev, "ipg");
 	if (IS_ERR(clk)) {
 		dev_err(&op->dev, "failed to lookup the clock!\n");
 		ret = PTR_ERR(clk);