drivers/gpu: Use kzalloc for allocating only one thing

Use kzalloc rather than kcalloc(1,...)

The use of the allocated memory that looks like an array is &p->relocs[0],
but this should be the same as p->relocs.

The semantic patch that makes this change is as follows:
(http://coccinelle.lip6.fr/)

// <smpl>
@@
@@

- kcalloc(1,
+ kzalloc(
          ...)
// </smpl>

Signed-off-by: Julia Lawall <julia@diku.dk>
Signed-off-by: Dave Airlie <airlied@redhat.com>