dm: gpio: Remove unused get_state() uclass method

This is no longer used so drop it.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/include/asm-generic/gpio.h b/include/asm-generic/gpio.h
index 8af760e..4ec411b 100644
--- a/include/asm-generic/gpio.h
+++ b/include/asm-generic/gpio.h
@@ -198,8 +198,6 @@
 	 * @return current function - GPIOF_...
 	 */
 	int (*get_function)(struct udevice *dev, unsigned offset);
-	int (*get_state)(struct udevice *dev, unsigned offset, char *state,
-			 int maxlen);
 };
 
 /**