drm/radeon: use kzalloc for allocating one thing

Use kzalloc for allocating one thing rather than
kcalloc(1...

The semantic patch that makes this change is as follows:

// <smpl>
@@
@@

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

Signed-off-by: Maninder Singh <maninder1.s@samsung.com>
Reviewed-by: Vaneet Narang <v.narang@samsung.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>