Input: soc_button_array - use gpio_is_valid()

gpio_keys will later use gpio_is_valid(). To match the actual
behavior, we should use it here too.

Signed-off-by: Benjamin Tissoires <[e-mail]>
Signed-off-by: Dmitry Torokhov <[e-mail]>

drivers/input/misc/soc_button_array.c

···
 #include <linux/acpi.h>
 #include <linux/gpio/consumer.h>
 #include <linux/gpio_keys.h>
+#include <linux/gpio.h>
 #include <linux/platform_device.h>
 
 /*
···
 			continue;
 
 		gpio = soc_button_lookup_gpio(&pdev->dev, info->acpi_index);
-		if (gpio < 0)
+		if (!gpio_is_valid(gpio))
 			continue;
 
 		gpio_keys[n_buttons].type = info->event_type;