UBI: provide LEB offset information

Provide the LEB offset information in the UBI device information data
structure. This piece of information is required by UBIFS to find out
what are the LEB offsets which are aligned to the max. write size.

If LEB offset not aligned to max. write size, then UBIFS has to take
this into account to write more optimally.

Signed-off-by: Artem Bityutskiy <[e-mail]>

drivers/mtd/ubi/kapi.c

···
 {
 	di->ubi_num = ubi->ubi_num;
 	di->leb_size = ubi->leb_size;
+	di->leb_start = ubi->leb_start;
 	di->min_io_size = ubi->min_io_size;
 	di->max_write_size = ubi->max_write_size;
 	di->ro_mode = ubi->ro_mode;

include/linux/mtd/ubi.h

···
  * struct ubi_device_info - UBI device description data structure.
  * @ubi_num: ubi device number
  * @leb_size: logical eraseblock size on this UBI device
+ * @leb_start: starting offset of logical eraseblocks within physical
+ *             eraseblocks
  * @min_io_size: minimal I/O unit size
  * @max_write_size: maximum amount of bytes the underlying flash can write at a
  *                  time (MTD write buffer size)
···
 struct ubi_device_info {
 	int ubi_num;
 	int leb_size;
+	int leb_start;
 	int min_io_size;
 	int max_write_size;
 	int ro_mode;