Negative -EINVAL was intended, not positive EINVAL.  Fix it.

Fixes: 95138e01 ("leds: pwm: Make error handling more robust")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/a33b981a-b2c4-4dc2-b00a-626a090d2f11@moroto.mountainSigned-off-by: Lee Jones <lee@kernel.org>