[ARM] make U300 clk_set_rate() return a _real_ errno

Another stupid instance of "return -1"-ism.
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/mach-u300/clock.c

@@ -682,7 +682,7 @@ int clk_set_rate(struct clk *clk, unsigned long rate)
 	} else {
 		printk(KERN_ERR "clock: Failed to set %s to %ld hz\n",
 		       clk->name, rate);
-		return -1;
+		return -EINVAL;
 	}
 }
 EXPORT_SYMBOL(clk_set_rate);