soc: bcm2835: Make !RASPBERRYPI_FIRMWARE dummies return failure

If CONFIG_RASPBERRYPI_FIRMWARE=n:

    drivers/gpio/gpio-raspberrypi-exp.c: In function ‘rpi_exp_gpio_get_polarity’:
    drivers/gpio/gpio-raspberrypi-exp.c:71: warning: ‘get.polarity’ is used uninitialized in this function
    drivers/gpio/gpio-raspberrypi-exp.c: In function ‘rpi_exp_gpio_get_direction’:
    drivers/gpio/gpio-raspberrypi-exp.c:150: warning: ‘get.direction’ is used uninitialized in this function

The dummy firmware interface functions return 0, which means success,
causing subsequent code to make use of the never initialized output
parameter.

Fix this by making the dummy functions return an error code (-ENOSYS)
instead.

Note that this assumes the firmware always fills in the requested data
in the CONFIG_RASPBERRYPI_FIRMWARE=y case.

Fixes: d45f1a56 ("staging: vc04_services: fix up rpi firmware functions")
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Reviewed-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>

include/soc/bcm2835/raspberrypi-firmware.h

@@ -143,13 +143,13 @@ struct rpi_firmware *rpi_firmware_get(struct device_node *firmware_node);
 static inline int rpi_firmware_property(struct rpi_firmware *fw, u32 tag,
 					void *data, size_t len)
 {
-	return 0;
+	return -ENOSYS;
 }
 
 static inline int rpi_firmware_property_list(struct rpi_firmware *fw,
 					     void *data, size_t tag_size)
 {
-	return 0;
+	return -ENOSYS;
 }
 
 static inline struct rpi_firmware *rpi_firmware_get(struct device_node *firmware_node)