drm/bridge: ti-sn65dsi86: Check the regmap return value when setting a GPIO

The ti_sn_bridge_gpio_set() got the return value of
regmap_update_bits() but didn't check it.  The function can't return
an error value, but we should at least print a warning if it didn't
work.

This fixes a compiler warning about setting "ret" but not using it.

Fixes: 27ed2b3f ("drm/bridge: ti-sn65dsi86: Export bridge GPIOs to Linux")
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200612123003.v2.4.Ia4376fd88cdc6e8f8b43c65548458305f82f1d61@changeid

drivers/gpu/drm/bridge/ti-sn65dsi86.c

@@ -999,6 +999,9 @@ static void ti_sn_bridge_gpio_set(struct gpio_chip *chip, unsigned int offset,
 	ret = regmap_update_bits(pdata->regmap, SN_GPIO_IO_REG,
 				 BIT(SN_GPIO_OUTPUT_SHIFT + offset),
 				 val << (SN_GPIO_OUTPUT_SHIFT + offset));
+	if (ret)
+		dev_warn(pdata->dev,
+			 "Failed to set bridge GPIO %u: %d\n", offset, ret);
 }
 
 static int ti_sn_bridge_gpio_direction_input(struct gpio_chip *chip,