gpu: drm: atomic_helper: Fix spelling errors

Trivial fixes identified while working on the DRM code.

  s/artifically/artificially/
  s/achive/achieve/

v2: - Actually spell achieve correctly!
Signed-off-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190312003307.14116-1-kieran.bingham+renesas@ideasonboard.com

drivers/gpu/drm/drm_atomic_helper.c

@@ -1752,7 +1752,7 @@ int drm_atomic_helper_commit(struct drm_device *dev,
 	 *
 	 * NOTE: Commit work has multiple phases, first hardware commit, then
 	 * cleanup. We want them to overlap, hence need system_unbound_wq to
-	 * make sure work items don't artifically stall on each another.
+	 * make sure work items don't artificially stall on each another.
 	 */
 
 	drm_atomic_state_get(state);
@@ -1786,7 +1786,7 @@ EXPORT_SYMBOL(drm_atomic_helper_commit);
  *
  * Asynchronous workers need to have sufficient parallelism to be able to run
  * different atomic commits on different CRTCs in parallel. The simplest way to
- * achive this is by running them on the &system_unbound_wq work queue. Note
+ * achieve this is by running them on the &system_unbound_wq work queue. Note
  * that drivers are not required to split up atomic commits and run an
  * individual commit in parallel - userspace is supposed to do that if it cares.
  * But it might be beneficial to do that for modesets, since those necessarily