nv50: fix drawing from tfb, direct-to-pushbuf submits

nv50: fix drawing from tfb, direct-to-pushbuf submits

The stride was being set to 0, which is illegal (and also non-sensical).
Also we must wait for the buffer to become available for reading as
otherwise a wrong value may be prefetched. Since we must wait for the
buffer anyways, and it's mapped and in GART, we may as well avoid the
annoyance of the indirect pushbuf submit.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Cc: mesa-stable@lists.freedesktop.org