trivial: fix then -> than typos in comments and documentation

- (better, more, bigger ...) then -> (...) than

Signed-off-by: Frederik Schwarzer <schwarzerf@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
diff --git a/include/mtd/ubi-user.h b/include/mtd/ubi-user.h
index ccdc562..2dc2eb2 100644
--- a/include/mtd/ubi-user.h
+++ b/include/mtd/ubi-user.h
@@ -253,7 +253,7 @@
  *
  * Re-sizing is possible for both dynamic and static volumes. But while dynamic
  * volumes may be re-sized arbitrarily, static volumes cannot be made to be
- * smaller then the number of bytes they bear. To arbitrarily shrink a static
+ * smaller than the number of bytes they bear. To arbitrarily shrink a static
  * volume, it must be wiped out first (by means of volume update operation with
  * zero number of bytes).
  */