leds: pwm-multicolor: Simplify an error message

dev_err_probe() already display the error code. There is no need to
duplicate it explicitly in the error message.

While at it, add a missing \n at the end of the message.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/07d35e221faaa380fd11cd4597e42354c8eb350c.1681576017.git.christophe.jaillet@wanadoo.fr