lib+mm: fix few spelling mistakes

All are in comments.

Signed-off-by: Bogdan Sikora <bsikora@redhat.com>
Cc: <linux-mm@kvack.org>
Cc: Rafael Aquini <aquini@redhat.com>
Cc: Kent Overstreet <kmo@daterainc.com>
Cc: Jan Kara <jack@suse.cz>
[jkosina@suse.cz: more fixup]
Acked-by: Rafael Aquini <aquini@redhat.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

lib/flex_proportions.c

@@ -17,7 +17,7 @@
  *
  *   \Sum_{j} p_{j} = 1,
  *
- * This formula can be straightforwardly computed by maintaing denominator
+ * This formula can be straightforwardly computed by maintaining denominator
  * (let's call it 'd') and for each event type its numerator (let's call it
  * 'n_j'). When an event of type 'j' happens, we simply need to do:
  *   n_j++; d++;

lib/percpu-refcount.c

@@ -12,7 +12,7 @@
  * particular cpu can (and will) wrap - this is fine, when we go to shutdown the
  * percpu counters will all sum to the correct value
  *
- * (More precisely: because moduler arithmatic is commutative the sum of all the
+ * (More precisely: because modular arithmetic is commutative the sum of all the
  * percpu_count vars will be equal to what it would have been if all the gets
  * and puts were done to a single integer, even if some of the percpu integers
  * overflow or underflow).