kobject: Transmit return value of call_usermodehelper() to caller

kobject_uevent_env() drops the return value of call_usermodehelper().
It will make upper caller, such as dm_send_uevents(), to lose error
information.

BTW, Previously kobject_uevent_env() transmitted return of
call_usermodehelper() to callers, but
commit	5f123fbd
"[PATCH] merge kobject_uevent and kobject_hotplug" removed it.
Signed-off-by: Wang Chen <wangchen@cn.fujitsu.com>
Cc: Kay Sievers <kay.sievers@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

lib/kobject_uevent.c

@@ -245,7 +245,8 @@ int kobject_uevent_env(struct kobject *kobj, enum kobject_action action,
 		if (retval)
 			goto exit;
 
-		call_usermodehelper(argv[0], argv, env->envp, UMH_WAIT_EXEC);
+		retval = call_usermodehelper(argv[0], argv,
+					     env->envp, UMH_WAIT_EXEC);
 	}
 
 exit: