drm/radeon: make rv770_set_sw_state failures non-fatal

On some cards it takes a relatively long time for the change
to take place.  Make a timeout non-fatal.

bug:
https://bugs.freedesktop.org/show_bug.cgi?id=76130

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org