leds: gpio: Add kernel log if devm_fwnode_gpiod_get() fails

leds: gpio: Add kernel log if devm_fwnode_gpiod_get() fails

In case leds-gpio fails to get at least one of possibly many GPIOs
from the DT (e.g. the GPIO is already requested) neither gpiolib nor
the driver does provide any helpful error log:

    leds-gpio: probe of leds failed with error -16

As the driver knows better how to handle errors with such mandatory
GPIOs, let's implement an error log which points to the affected
GPIO.

Signed-off-by: Stefan Wahren <wahrenst@gmx.net>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20231202183636.7055-1-wahrenst@gmx.net
Signed-off-by: Lee Jones <lee@kernel.org>