drm/nouveau/mmu/gp100: remove unused variable

Fixes a compilation issue introduced because I forgot to test with WERROR
enabled.

Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: DRI <dri-devel@lists.freedesktop.org>
Cc: nouveau@lists.freedesktop.org
Fixes: 404046c ("drm/nouveau/mmu/gp100-: drop unneeded assignment in the if condition.")
Acked-by: Adam Jackson <ajax@redhat.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Karol Herbst <kherbst@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211012133334.1737918-1-kherbst@redhat.com

drivers/gpu/drm/nouveau/nvkm/subdev/mmu/vmmgp100.c

@@ -488,7 +488,7 @@ gp100_vmm_fault_cancel(struct nvkm_vmm *vmm, void *argv, u32 argc)
 		struct gp100_vmm_fault_cancel_v0 v0;
 	} *args = argv;
 	int ret = -ENOSYS;
-	u32 inst, aper;
+	u32 aper;
 
 	if ((ret = nvif_unpack(ret, &argv, &argc, args->v0, 0, 0, false)))
 		return ret;