drm/nouveau: fix nv04_sgdma_bind on non-"4kB pages" archs

nv04_sgdma_bind binds the same page multiple times on
architectures where PAGE_SIZE != 4096.
Let's fix it.

Signed-off-by: Marcin Slusarz <marcin.slusarz@gmail.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>