driver core: dd: fix return value of __setup handler

When "driver_async_probe=nulltty" is used on the kernel boot command line,
it causes an Unknown parameter message and the string is added to init's
environment strings, polluting them.

  Unknown kernel command line parameters "BOOT_IMAGE=/boot/bzImage-517rc6
  driver_async_probe=nulltty", will be passed to user space.

 Run /sbin/init as init process
   with arguments:
     /sbin/init
   with environment:
     HOME=/
     TERM=linux
     BOOT_IMAGE=/boot/bzImage-517rc6
     driver_async_probe=nulltty

Change the return value of the __setup function to 1 to indicate
that the __setup option has been handled.

Link: lore.kernel.org/r/[email protected]
Fixes: 1ea61b6 ("async: Add cmdline option to specify drivers to be async probed")
Cc: Feng Tang <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: "Rafael J. Wysocki" <[email protected]>
Reported-by: Igor Zhbanov <[email protected]>
Reviewed-by: Feng Tang <[email protected]>
Signed-off-by: Randy Dunlap <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: rddunlap

drivers/base/dd.c

@@ -806,7 +806,7 @@ static int __init save_async_options(char *buf)
 		pr_warn("Too long list of driver names for 'driver_async_probe'!\n");
 
 	strlcpy(async_probe_drv_names, buf, ASYNC_DRV_NAMES_MAX_LEN);
-	return 0;
+	return 1;
 }
 __setup("driver_async_probe=", save_async_options);