drm/i915: Use actual readout results for .get_freq()

drm/i915: Use actual readout results for .get_freq()

Currently the DPLL .get_freq() uses pll->state.hw_state which
is not the thing we actually read out (except during driver
load/resume). Outside of that pll->state.hw_state is just the
thing we committed last time around. During state check we
just read the thing into crtc_state->dpll_hw_state, so that
is what we should use for calculating the DPLL output frequency.

I think we used to do this so that the results of the readout
were actually used, but somehow it got changed when the
.get_freq() refactoring happened.

Cc: Imre Deak <imre.deak@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201109231239.17002-3-ville.syrjala@linux.intel.com
Reviewed-by: Imre Deak <imre.deak@intel.com>