drm/nouveau: fix relocations applying logic and a double-free

drm/nouveau: fix relocations applying logic and a double-free

Commit 03e0d26fcf79 ("drm/nouveau: slowpath for pushbuf ioctl") included
a logic-bug which results in the relocations not actually getting
applied at all as the call to nouveau_gem_pushbuf_reloc_apply() is
never reached. This causes a regression with graphical corruption,
triggered when relocations need to be done (for example after a
suspend/resume cycle.)

Fix by setting *apply_relocs value only if there were more than 0
relocations.

Additionally, the never reached code had a leftover u_free() call,
which, after fixing the logic, now got called and resulted in a
double-free. Fix by removing one u_free(), moving the other
and adding check for errors.

Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Ben Skeggs <bskeggs@redhat.com>
Cc: nouveau@lists.freedesktop.org
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Matti Hamalainen <ccr@tnsp.org>
Fixes: 03e0d26fcf79 ("drm/nouveau: slowpath for pushbuf ioctl")
References: https://gitlab.freedesktop.org/drm/nouveau/-/issues/11
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20201120152338.1203257-1-ccr@tnsp.org