drm/nouveau/kms: delete an useless function call in nouveau_framebuffer_new()

nouveau_framebuffer_new() call drm_format_info_plane_width() to get a width
of plane, but width is not used then, so it's a useless function call here.

Signed-off-by: Luo Jiaxing <luojiaxing@huawei.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