[ACPI] acpi_system_write_wakeup_device() has the wrong return type

and is missing the __user attribution from its buffer argument.
This patch shuts up the resulting warnings on x86-64.

From: William Lee Irwin III <wli@holomorphy.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>

drivers/acpi/sleep/proc.c

@@ -384,10 +384,10 @@ acpi_system_wakeup_device_seq_show(struct seq_file *seq, void *offset)
 	return 0;
 }
 
-static int
+static ssize_t
 acpi_system_write_wakeup_device (
 	struct file		*file,
-	const char		*buffer,
+	const char __user	*buffer,
 	size_t			count,
 	loff_t			*ppos)
 {