UBIFS: introduce a helpful variable

This patch introduces a helpful @c->idx_leb_size variable.
The patch also fixes some spelling issues and makes comments
use "LEB" instead of "eraseblock", which is more correct.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
diff --git a/fs/ubifs/ubifs.h b/fs/ubifs/ubifs.h
index 2da1193..a53b9a6 100644
--- a/fs/ubifs/ubifs.h
+++ b/fs/ubifs/ubifs.h
@@ -1015,6 +1015,8 @@
  * @min_io_shift: number of bits in @min_io_size minus one
  * @leb_size: logical eraseblock size in bytes
  * @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)
  * @leb_cnt: count of logical eraseblocks
  * @max_leb_cnt: maximum count of logical eraseblocks
  * @old_leb_cnt: count of logical eraseblocks before re-size
@@ -1132,8 +1134,8 @@
  *             previous commit start
  * @uncat_list: list of un-categorized LEBs
  * @empty_list: list of empty LEBs
- * @freeable_list: list of freeable non-index LEBs (free + dirty == leb_size)
- * @frdi_idx_list: list of freeable index LEBs (free + dirty == leb_size)
+ * @freeable_list: list of freeable non-index LEBs (free + dirty == @leb_size)
+ * @frdi_idx_list: list of freeable index LEBs (free + dirty == @leb_size)
  * @freeable_cnt: number of freeable LEBs in @freeable_list
  *
  * @ltab_lnum: LEB number of LPT's own lprops table
@@ -1253,6 +1255,7 @@
 	int min_io_shift;
 	int leb_size;
 	int half_leb_size;
+	int idx_leb_size;
 	int leb_cnt;
 	int max_leb_cnt;
 	int old_leb_cnt;