Use calloc instead of malloc/memset-0

Use calloc instead of malloc/memset-0

This patch has been generated by the following Coccinelle semantic
patch:

@@
expression E;
identifier I;
@@
- I = malloc(E);
+ I = calloc(1, E);
...
- memset(I, 0, sizeof *I);

Reviewed-by: Brian Paul <brianp@vmware.com>