drivers/misc/ep93xx_pwm.c: world-writable sysfs files

Don't allow everybody to change device settings.

Signed-off-by: Vasiliy Kulikov <segoon@openwall.com>
Acked-by: Hartley Sweeten <hartleys@visionengravers.com>
Cc: Matthieu Crapet <mcrapet@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>