kvmalloc_array + __GFP_ZERO is the same with kvcalloc.

Fixes the below:
drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c:873 amdgpu_cs_parser_bos() warn: Please consider using kvcalloc instead of kvmalloc_array

Cc: Christian König <christian.koenig@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>