drm/nouveau/nouveau_bo: Remove unused variables 'dev'

Fixes the following W=1 kernel build warning(s):

 drivers/gpu/drm/nouveau/nouveau_bo.c: In function ‘nouveau_ttm_tt_populate’:
 drivers/gpu/drm/nouveau/nouveau_bo.c:1228:17: warning: variable ‘dev’ set but not used [-Wunused-but-set-variable]
 drivers/gpu/drm/nouveau/nouveau_bo.c: In function ‘nouveau_ttm_tt_unpopulate’:
 drivers/gpu/drm/nouveau/nouveau_bo.c:1252:17: warning: variable ‘dev’ set but not used [-Wunused-but-set-variable]

Cc: Ben Skeggs <bskeggs@redhat.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: Jeremy Kolb <jkolb@brandeis.edu>
Cc: dri-devel@lists.freedesktop.org
Cc: nouveau@lists.freedesktop.org
Cc: linux-media@vger.kernel.org
Cc: linaro-mm-sig@lists.linaro.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Reviewed-by: Karol Herbst <kherbst@redhat.com>
Signed-off-by: Karol Herbst <kherbst@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210416143725.2769053-8-lee.jones@linaro.org