drm/nouveau: Remove unused variable ret

Fix the following coccicheck warnings:

./drivers/gpu/drm/nouveau/nouveau_bios.c:2048:5-8: Unneeded variable:
"ret". Return "0" on line 2061.

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Reviewed-by: Karol Herbst <kherbst@redhat.com>
Signed-off-by: Karol Herbst <kherbst@redhat.com>
Link: https://gitlab.freedesktop.org/drm/nouveau/-/merge_requests/10