[PATCH] acpi/button.c: fix defined but not used warning

[Randy Dunlap]

From: Randy Dunlap <rdun...@infradead.org>

Fix a build warning in the ACPI button driver when CONFIG_PROC_FS
is not enabled by marking the unused function as __maybe_unused.

../drivers/acpi/button.c:252:12: warning: 'acpi_button_state_seq_show' defined 
but not used [-Wunused-function]

Signed-off-by: Randy Dunlap <rdun...@infradead.org>
Cc: "Rafael J. Wysocki" <r...@rjwysocki.net>
Cc: Len Brown <l...@kernel.org>
Cc: linux-a...@vger.kernel.org
---
 drivers/acpi/button.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- linux-next-20180706.orig/drivers/acpi/button.c
+++ linux-next-20180706/drivers/acpi/button.c
@@ -21,6 +21,7 @@
 
 #define pr_fmt(fmt) "ACPI: button: " fmt
 
+#include <linux/compiler.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/init.h>
@@ -249,7 +250,8 @@ static int acpi_lid_notify_state(struct
        return ret;
 }
 
-static int acpi_button_state_seq_show(struct seq_file *seq, void *offset)
+static int __maybe_unused acpi_button_state_seq_show(struct seq_file *seq,
+                                                    void *offset)
 {
        struct acpi_device *device = seq->private;
        int state;