drm/i915/fbc: Remember to update FBC state even when not reallocating CFB

We mustn't forget to update our FBC state even if we don't have
to reallocate the CFB. Otherwise we won't refresh our notion
of what eg. the new fence or the new override CFB stride
should be. Using the wrong CFB stride in particular can cause
underruns and could even corrupt other stuff in stolen.

Fixes: f4cfdbb0 ("drm/i915/fbc: Nuke state_cache")
Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/4774


Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211216110822.8461-1-ville.syrjala@linux.intel.com


Reviewed-by: Mika Kahola <mika.kahola@intel.com>
(cherry picked from commit 798c5daf)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>