drivers/video/backlight/apple_bl.c: include header for exported symbol prototypes

Include the header to pickup the exported symbol prototype.

Quiets the sparse warning:

  warning: symbol 'apple_bl_register' was not declared. Should it be static?
  warning: symbol 'apple_bl_unregister' was not declared. Should it be static?

[akpm@linux-foundation.org: fix resulting build error]
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Richard Purdie <rpurdie@rpsys.net>
Signed-off-by: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/video/backlight/apple_bl.c

@@ -25,6 +25,7 @@
 #include <linux/pci.h>
 #include <linux/acpi.h>
 #include <linux/atomic.h>
+#include <linux/apple_bl.h>
 
 static struct backlight_device *apple_backlight_device;
 

include/linux/apple_bl.h

@@ -5,7 +5,7 @@
 #ifndef _LINUX_APPLE_BL_H
 #define _LINUX_APPLE_BL_H
 
-#ifdef CONFIG_BACKLIGHT_APPLE
+#if defined(CONFIG_BACKLIGHT_APPLE) || defined(CONFIG_BACKLIGHT_APPLE_MODULE)
 
 extern int apple_bl_register(void);
 extern void apple_bl_unregister(void);