ARM: OMAP: Fix warnings in leds-omap-pwm.c:

drivers/leds/leds-omap-pwm.c: In function 'omap_pwm_led_probe':
drivers/leds/leds-omap-pwm.c:260: warning: ignoring return
value of 'class_device_create_file', declared with attribute
warn_unused_result
drivers/leds/leds-omap-pwm.c:262: warning: ignoring return
value of 'class_device_create_file', declared with attribute
warn_unused_result

Signed-off-by: Dirk Behme <dirk.behme_at_gmail.com>