[ARM] S3C24XX: GPIO: Fix error returns from gpio functions

Several GPIO functions have been returning -1 to indicate
an error instead of returning a proper error code. Change
to return -EINVAL for invalid argument(s).

Signed-off-by: Ben Dooks <ben-linux@fluff.org>

arch/arm/mach-s3c2410/gpio.c

@@ -40,7 +40,7 @@ int s3c2410_gpio_irqfilter(unsigned int pin, unsigned int on,
 	unsigned long val;
 
 	if (pin < S3C2410_GPG(8) || pin > S3C2410_GPG(15))
-		return -1;
+		return -EINVAL;
 
 	config &= 0xff;