lib+mm: fix few spelling mistakes

All are in comments.
Signed-off-by: NBogdan 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: NRafael Aquini <aquini@redhat.com>
Signed-off-by: NJiri Slaby <jslaby@suse.cz>
Signed-off-by: NJiri 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).

mm/balloon_compaction.c

@@ -13,10 +13,10 @@
 /*
  * balloon_page_enqueue - allocates a new page and inserts it into the balloon
  *			  page list.
- * @b_dev_info: balloon device decriptor where we will insert a new page to
+ * @b_dev_info: balloon device descriptor where we will insert a new page to
  *
  * Driver must call it to properly allocate a new enlisted balloon page
- * before definetively removing it from the guest system.
+ * before definitively removing it from the guest system.
  * This function returns the page address for the recently enqueued page or
  * NULL in the case we fail to allocate a new page this turn.
  */