drivers/mtd/devices/docg3.c: avoid world-writable sysfs files.

In line with practice for module parameters, we're adding a build-time
check that sysfs files aren't world-writable.

Cc: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
diff --git a/drivers/mtd/devices/docg3.c b/drivers/mtd/devices/docg3.c
index dd5e101..91a169c 100644
--- a/drivers/mtd/devices/docg3.c
+++ b/drivers/mtd/devices/docg3.c
@@ -1608,8 +1608,8 @@
 #define FLOOR_SYSFS(id) { \
 	__ATTR(f##id##_dps0_is_keylocked, S_IRUGO, dps0_is_key_locked, NULL), \
 	__ATTR(f##id##_dps1_is_keylocked, S_IRUGO, dps1_is_key_locked, NULL), \
-	__ATTR(f##id##_dps0_protection_key, S_IWUGO, NULL, dps0_insert_key), \
-	__ATTR(f##id##_dps1_protection_key, S_IWUGO, NULL, dps1_insert_key), \
+	__ATTR(f##id##_dps0_protection_key, S_IWUSR|S_IWGRP, NULL, dps0_insert_key), \
+	__ATTR(f##id##_dps1_protection_key, S_IWUSR|S_IWGRP, NULL, dps1_insert_key), \
 }
 
 static struct device_attribute doc_sys_attrs[DOC_MAX_NBFLOORS][4] = {