cmd: gpio: Make `gpio input` return pin value again

4dbc107f4683 ("cmd: gpio: Correct do_gpio() return value") correctly
changed the behaviour of the gpio command to return CMD_RET_SUCCESS or
CMD_RET_FAILURE, but any existing script which expects the return value
to be the pin value is broken by this change.

Reinstate the legacy behaviour for `gpio input` only.

Fixes: 4dbc107f4683 ("cmd: gpio: Correct do_gpio() return value")
Signed-off-by: Alex Kiernan <alex.kiernan@gmail.com>
Signed-off-by: Alex Kiernan <alex.kiernan@hivehome.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/cmd/gpio.c b/cmd/gpio.c
index 16c2ceb..408a942 100644
--- a/cmd/gpio.c
+++ b/cmd/gpio.c
@@ -248,7 +248,12 @@
 	if (ret != -EBUSY)
 		gpio_free(gpio);
 
-	return CMD_RET_SUCCESS;
+	/*
+	 * Whilst wrong, the legacy gpio input command returns the pin
+	 * value, or CMD_RET_FAILURE (which is indistinguishable from a
+	 * valid pin value).
+	 */
+	return (sub_cmd == GPIOC_INPUT) ? value : CMD_RET_SUCCESS;
 
 err:
 	if (ret != -EBUSY)