mm: use kcalloc() instead of kzalloc() to allocate array

mm: use kcalloc() instead of kzalloc() to allocate array

The advantage of kcalloc is, that will prevent integer overflows which
could result from the multiplication of number of elements and size and it
is also a bit nicer to read.

The semantic patch that makes this change is available
in https://lkml.org/lkml/2011/11/25/107

Signed-off-by: Thomas Meyer <thomas@m3y3r.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>