drm/i915: Actually set the reset bit in i965_reset.

Previously, it was only being set if passed GDRST_FULL - but the only
caller passed GDRST_RENDER.  So the hardware never actually reset.
The comments also did not match the code.

Instead, just set the reset bit regardless of what flags were passed.
The GPU now resets correctly on my GM45.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>