driver core: cpu: fix section mismatch in cpu.c:store_online

Fix following warning:
WARNING: vmlinux.o(.text+0x64609c): Section mismatch in reference from the function store_online() to the function .cpuinit.text:cpu_up()

store_online() is defined inside a HOTPLUG_CPU block so references are OK. 
Ignore references by annotating store_online() with __ref.

Note: This is needed because cpu_up() most likely should not have been
__cpuinit but all the hotplug cpu code misuses the __cpuinit annotation.
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/base/cpu.c

@@ -28,7 +28,7 @@ static ssize_t show_online(struct sys_device *dev, char *buf)
 	return sprintf(buf, "%u\n", !!cpu_online(cpu->sysdev.id));
 }
 
-static ssize_t store_online(struct sys_device *dev, const char *buf,
+static ssize_t __ref store_online(struct sys_device *dev, const char *buf,
 			    size_t count)
 {
 	struct cpu *cpu = container_of(dev, struct cpu, sysdev);
@@ -55,7 +55,7 @@ static ssize_t store_online(struct sys_device *dev, const char *buf,
 }
 static SYSDEV_ATTR(online, 0644, show_online, store_online);
 
-static void __devinit register_cpu_control(struct cpu *cpu)
+static void __cpuinit register_cpu_control(struct cpu *cpu)
 {
 	sysdev_create_file(&cpu->sysdev, &attr_online);
 }