can: build proc support only if CONFIG_PROC_FS is activated

When building can subsystem with CONFIG_PROC_FS=n I detected some unused
variables warning by using proc functions. In CAN the proc handling is
nicely placed in one object file. This patch adds simple add a
dependency on CONFIG_PROC_FS for CAN's proc.o file and corresponding
static inline no-op functions.

Signed-off-by: Alexander Aring <aar@pengutronix.de>
Acked-by: Oliver Hartkopp <socketcan@hartkopp.net>
[mkl: provide static inline noops instead of using #ifdefs]
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
diff --git a/net/can/proc.c b/net/can/proc.c
index 1a19b98..85ef7bb 100644
--- a/net/can/proc.c
+++ b/net/can/proc.c
@@ -517,8 +517,7 @@
 	can_dir = proc_mkdir("can", init_net.proc_net);
 
 	if (!can_dir) {
-		printk(KERN_INFO "can: failed to create /proc/net/can . "
-		       "CONFIG_PROC_FS missing?\n");
+		pr_info("can: failed to create /proc/net/can.\n");
 		return;
 	}