lib: bitmap: fix typo in kerneldoc for bitmap_pos_to_ord

A few lines above, it was stated that positions for non-set bits are
mapped to -1, which is obviously also what the code does.
Signed-off-by: NRasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

lib/bitmap.c

@@ -712,7 +712,7 @@ EXPORT_SYMBOL(bitmap_parselist_user);
  *
  * If for example, just bits 4 through 7 are set in @buf, then @pos
  * values 4 through 7 will get mapped to 0 through 3, respectively,
- * and other @pos values will get mapped to 0.  When @pos value 7
+ * and other @pos values will get mapped to -1.  When @pos value 7
  * gets mapped to (returns) @ord value 3 in this example, that means
  * that bit 7 is the 3rd (starting with 0th) set bit in @buf.
  *