ARM: SAMSUNG: remove duplicated header include

This patch removes duplicated slab header for pwm backlight.
arch/arm/plat-samsung/dev-backlight.c: slab.h is included
more than once.
Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>

arch/arm/plat-samsung/dev-backlight.c

@@ -15,7 +15,6 @@
 #include <linux/slab.h>
 #include <linux/io.h>
 #include <linux/pwm_backlight.h>
-#include <linux/slab.h>
 
 #include <plat/devs.h>
 #include <plat/gpio-cfg.h>