drm/amdgpu: Use kzalloc instead of kmalloc+__GFP_ZERO in amdgpu_ras.c

Fixes the below smatch warnings:

drivers/gpu/drm/amd/amdgpu/amdgpu_ras.c:2543 amdgpu_ras_recovery_init() warn: Please consider using kzalloc instead of kmalloc
drivers/gpu/drm/amd/amdgpu/amdgpu_ras.c:2830 amdgpu_ras_init() warn: Please consider using kzalloc instead of kmalloc

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: Tao Zhou <tao.zhou1@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>