nv30: avoid doing extra work on clear and hitting unexpected states

nv30: avoid doing extra work on clear and hitting unexpected states

Clearing can happen at a time when various state objects are incoherent
and not ready for a draw. Some of the validation functions don't handle
this well, so only flush the framebuffer state. This has the advantage
of also not doing extra work.

This works around some crashes that can happen when clearing.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Tobias Klausmann <tobias.johannes.klausmann@mni.thm.de>
(cherry picked from commit aba3392541f38f82e3ebde251fdcca78e90adbf3)