staging: greybus: svc_watchdog: replace printk() with pr_err()

Fix coding style issue caught by checkpatch.pl related to the following
warning:
	- "WARNING: Prefer [subsystem eg: netdev]_err([subsystem]dev, ... then
dev_err(dev, ... then pr_err(...  to printk(KERN_ERR ."
Signed-off-by: Emmanuil Chatzipetru <chatzi.emanuel@gmail.com>
Acked-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/greybus/svc_watchdog.c

@@ -56,7 +56,7 @@ static void greybus_reset(struct work_struct *work)
 		NULL,
 	};
 
-	printk(KERN_ERR "svc_watchdog: calling \"%s %s\" to reset greybus network!\n",
+	pr_err("svc_watchdog: calling \"%s %s\" to reset greybus network!\n",
 	       argv[0], argv[1]);
 	call_usermodehelper(start_path, argv, envp, UMH_WAIT_EXEC);
 }