drm/nouveau: fix error path in nvkm_gsp_fwsec_v2

drm/nouveau: fix error path in nvkm_gsp_fwsec_v2

Function nvkm_gsp_fwsec_v2() sets 'ret' if the kmemdup() call fails, but
it never uses or returns 'ret' after that point.  We always need to release
the firmware regardless, so do that and then check for error.

Fixes: 176fdcbddfd2 ("drm/nouveau/gsp/r535: add support for booting GSP-RM")
Cc: stable@vger.kernel.org # v6.7+
Signed-off-by: Timur Tabi <ttabi@nvidia.com>
Link: https://lore.kernel.org/r/20250813001004.2986092-1-ttabi@nvidia.com
Signed-off-by: Danilo Krummrich <dakr@kernel.org>