powerpc/mpc5121: fix NULL test in mpc5121_clk_get utility function.

strcmp on NULL results in a segmentation fault, also, remove the second,
redundant test on dev

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

arch/powerpc/platforms/512x/clock.c

@@ -56,12 +56,12 @@ static struct clk *mpc5121_clk_get(struct device *dev, const char *id)
 	int dev_match = 0;
 	int id_match = 0;
 
-	if (dev == NULL && id == NULL)
+	if (dev == NULL || id == NULL)
 		return NULL;
 
 	mutex_lock(&clocks_mutex);
 	list_for_each_entry(p, &clocks, node) {
-		if (dev && dev == p->dev)
+		if (dev == p->dev)
 			dev_match++;
 		if (strcmp(id, p->name) == 0)
 			id_match++;