drm/amd: Use `amdgpu_ucode_release` helper for si

The `amdgpu_ucode_release` helper is replacing all calls
to release_firmware.

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>