ARM: omap1/ams-delta: warn about failed regulator enable

The modem pm handler in the ams-delta board uses regulator_enable()
but does not check for a successful return code:

board-ams-delta.c:521:3: error: ignoring return value of 'regulator_enable', declared with attribute warn_unused_result [-Werror=unused-result]

It is not easy to propagate that return code to the callers in
uart_configure_port/uart_suspend_port/uart_resume_port, unless
we change all UART drivers, and it is unclear what those would
do with the return code.

Instead, this patch uses a runtime warning to replace the
compiletime warning. I have checked that the regulator in question
is hardcoded to a fixed-voltage GPIO regulator, and that should
never fail to get enabled if I understand the code right.

Acked-by: Tony Lindgren <tony@atomide.com>
Acked-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Link: https://patchwork.kernel.org/patch/8391981/
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

arch/arm/mach-omap1/board-ams-delta.c

@@ -510,6 +510,7 @@ static void __init ams_delta_init(void)
 static void modem_pm(struct uart_port *port, unsigned int state, unsigned old)
 {
 	struct modem_private_data *priv = port->private_data;
+	int ret;
 
 	if (IS_ERR(priv->regulator))
 		return;
@@ -518,9 +519,16 @@ static void modem_pm(struct uart_port *port, unsigned int state, unsigned old)
 		return;
 
 	if (state == 0)
-		regulator_enable(priv->regulator);
+		ret = regulator_enable(priv->regulator);
 	else if (old == 0)
-		regulator_disable(priv->regulator);
+		ret = regulator_disable(priv->regulator);
+	else
+		ret = 0;
+
+	if (ret)
+		dev_warn(port->dev,
+			 "ams_delta modem_pm: failed to %sable regulator: %d\n",
+			 state ? "dis" : "en", ret);
 }
 
 static struct plat_serial8250_port ams_delta_modem_ports[] = {