kgdboc: fix return value of __setup handler

__setup() handlers should return 1 to obsolete_checksetup() in
init/main.c to indicate that the boot option has been handled.
A return of 0 causes the boot option/value to be listed as an Unknown
kernel parameter and added to init's (limited) environment strings.
So return 1 from kgdboc_option_setup().

Unknown kernel command line parameters "BOOT_IMAGE=/boot/bzImage-517rc7
  kgdboc=kbd kgdbts=", 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-517rc7
     kgdboc=kbd
     kgdbts=

Link: lore.kernel.org/r/[email protected]
Fixes: 1bd54d8 ("kgdboc: Passing ekgdboc to command line causes panic")
Fixes: f2d937f ("consoles: polling support, kgdboc")
Cc: He Zhe <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Jiri Slaby <[email protected]>
Cc: [email protected]
Cc: Jason Wessel <[email protected]>
Cc: Daniel Thompson <[email protected]>
Cc: Douglas Anderson <[email protected]>
Cc: [email protected]
Reported-by: Igor Zhbanov <[email protected]>
Reviewed-by: Douglas Anderson <[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/tty/serial/kgdboc.c

@@ -403,16 +403,16 @@ static int kgdboc_option_setup(char *opt)
 {
 	if (!opt) {
 		pr_err("config string not provided\n");
-		return -EINVAL;
+		return 1;
 	}
 
 	if (strlen(opt) >= MAX_CONFIG_LEN) {
 		pr_err("config string too long\n");
-		return -ENOSPC;
+		return 1;
 	}
 	strcpy(config, opt);
 
-	return 0;
+	return 1;
 }
 
 __setup("kgdboc=", kgdboc_option_setup);