leds: leds-pwm: return proper error if pwm_request failed

Return PTR_ERR(led_dat->pwm) instead of 0 if pwm_request failed

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Cc: Richard Purdie <rpurdie@rpsys.net>
Cc: Luotao Fu <l.fu@pengutronix.de>
Cc: Reviewed-by: Dmitry Torokhov <dtor@mail.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>