drm/i915: Fix the docs for intel_set_cdclk_post_plane_update()

s/before/after/ again after accidentally changing it the
other way in commit 5604e9ce ("drm/i915: Simplify
intel_set_cdclk_{pre,post}_plane_update() calling convention")

Cc: José Roberto de Souza <jose.souza@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200204154803.25403-1-ville.syrjala@linux.intel.comReviewed-by: José Roberto de Souza <jose.souza@intel.com>

drivers/gpu/drm/i915/display/intel_cdclk.c

@@ -1907,7 +1907,7 @@ intel_set_cdclk_pre_plane_update(struct intel_atomic_state *state)
  * intel_set_cdclk_post_plane_update - Push the CDCLK state to the hardware
  * @state: intel atomic state
  *
- * Program the hardware before updating the HW plane state based on the
+ * Program the hardware after updating the HW plane state based on the
  * new CDCLK state, if necessary.
  */
 void