UBI: incorporate LEB offset information

Incorporate the LEB offset information into UBIFS. We'll use this
information in one of the next patches to figure out what are the
max. write size offsets relative to the PEB. So this patch is just
a preparation.
Signed-off-by: NArtem Bityutskiy <Artem.Bityutskiy@nokia.com>

fs/ubifs/super.c

@@ -504,6 +504,7 @@ static int init_constants_early(struct ubifs_info *c)
 
 	c->leb_cnt = c->vi.size;
 	c->leb_size = c->vi.usable_leb_size;
+	c->leb_start = c->di.leb_start;
 	c->half_leb_size = c->leb_size / 2;
 	c->min_io_size = c->di.min_io_size;
 	c->min_io_shift = fls(c->min_io_size) - 1;

fs/ubifs/ubifs.h

@@ -1028,6 +1028,8 @@ struct ubifs_debug_info;
  *                  time (MTD write buffer size)
  * @max_write_shift: number of bits in @max_write_size minus one
  * @leb_size: logical eraseblock size in bytes
+ * @leb_start: starting offset of logical eraseblocks within physical
+ *             eraseblocks
  * @half_leb_size: half LEB size
  * @idx_leb_size: how many bytes of an LEB are effectively available when it is
  *                used to store indexing nodes (@leb_size - @max_idx_node_sz)
@@ -1276,6 +1278,7 @@ struct ubifs_info {
 	int max_write_size;
 	int max_write_shift;
 	int leb_size;
+	int leb_start;
 	int half_leb_size;
 	int idx_leb_size;
 	int leb_cnt;