CVE-2024-56752 drm/nouveau/gr/gf100: Fix missing unlock in gf100_gr_chan_new()

In the Linux kernel, the following vulnerability has been resolved: drm/nouveau/gr/gf100: Fix missing unlock in gf100grchannew When the call to gf100grctxgenerate fails, unlock gr-fecs.mutex before returning the error. Fixes smatch warning: drivers/gpu/drm/nouveau/nvkm/engine/gr/gf100.c:480...