gpio-pca953x: fix gpio_base

gpio_base was set to 0 if no system platform data or open firmware
platform data was provided. This led to conflicts, if any other gpiochip
with a gpiobase of 0 was instantiated already. Setting it to -1 will
automatically use the first one available.
Signed-off-by: Hartmut Knaack <knaack.h@gmx.de>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

drivers/gpio/gpio-pca953x.c

@@ -577,6 +577,7 @@ pca953x_get_alt_pdata(struct i2c_client *client, int *gpio_base, int *invert)
 void
 pca953x_get_alt_pdata(struct i2c_client *client, int *gpio_base, int *invert)
 {
+	*gpio_base = -1;
 }
 #endif