drm/i915: s/pre_empemph/preemph/

I managed to fumble some functions names. Fix them.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200929233449.32323-2-ville.syrjala@linux.intel.com


Reviewed-by: Imre Deak <imre.deak@intel.com>