`vol' is a newly allocated value by kzalloc. Initialize it by assignment
instead of `+='.
Signed-off-by: Sheng Yong <shengyong1@huawei.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
 
        /* Calculate how many eraseblocks are requested */
        vol->usable_leb_size = ubi->leb_size - ubi->leb_size % req->alignment;
-       vol->reserved_pebs += div_u64(req->bytes + vol->usable_leb_size - 1,
-                                     vol->usable_leb_size);
+       vol->reserved_pebs = div_u64(req->bytes + vol->usable_leb_size - 1,
+                                    vol->usable_leb_size);
 
        /* Reserve physical eraseblocks */
        if (vol->reserved_pebs > ubi->avail_pebs) {