drm/amdgpu/sriov:fix memory leak after gpu reset

GPU reset will require all hw doing hw_init thus
ucode_init_bo will be invoked again, which lead to
memory leak

skip the fw_buf allocation during sriov gpu reset to avoid
memory leak.

Signed-off-by: Monk Liu <Monk.Liu@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>