drm/amdgpu: Fix memory leak in amdgpu_cs_pass1

When p->gang_size equals 0, amdgpu_cs_pass1() will return directly
without freeing chunk_array, which will cause a memory leak issue,
this patch fixes it.

Fixes: 4624459c ("drm/amdgpu: add gang submit frontend v6")
Reviewed-by: Luben Tuikov <luben.tuikov@amd.com>
Signed-off-by: Dong Chenchen <dongchenchen2@huawei.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>