[ARM] S3C: BUG_ON() if clock has already been registered

Add a simple check when registering a clock on whether
the clock has already been added to the list.

Any attempt to re-register a clock will cause the
clock list to be come looped and thus produces silent
failures when looking up clocks.
Signed-off-by: NBen Dooks <ben-linux@fluff.org>

arch/arm/plat-s3c/clock.c

@@ -304,6 +304,9 @@ int s3c24xx_register_clock(struct clk *clk)
 
 	/* add to the list of available clocks */
 
+	/* Quick check to see if this clock has already been registered. */
+	BUG_ON(clk->list.prev != clk->list.next);
+
 	spin_lock(&clocks_lock);
 	list_add(&clk->list, &clocks);
 	spin_unlock(&clocks_lock);