Fix common misspellings

Fixes generated by 'codespell' and manually reviewed.

Signed-off-by: Lucas De Marchi <lucas.demarchi@profusion.mobi>
diff --git a/include/drm/ttm/ttm_bo_api.h b/include/drm/ttm/ttm_bo_api.h
index 50852aa..94e2ce4 100644
--- a/include/drm/ttm/ttm_bo_api.h
+++ b/include/drm/ttm/ttm_bo_api.h
@@ -50,10 +50,10 @@
  *
  * @fpfn:		first valid page frame number to put the object
  * @lpfn:		last valid page frame number to put the object
- * @num_placement:	number of prefered placements
- * @placement:		prefered placements
- * @num_busy_placement:	number of prefered placements when need to evict buffer
- * @busy_placement:	prefered placements when need to evict buffer
+ * @num_placement:	number of preferred placements
+ * @placement:		preferred placements
+ * @num_busy_placement:	number of preferred placements when need to evict buffer
+ * @busy_placement:	preferred placements when need to evict buffer
  *
  * Structure indicating the placement you request for an object.
  */
@@ -160,7 +160,7 @@
  * @mem: structure describing current placement.
  * @persistant_swap_storage: Usually the swap storage is deleted for buffers
  * pinned in physical memory. If this behaviour is not desired, this member
- * holds a pointer to a persistant shmem object.
+ * holds a pointer to a persistent shmem object.
  * @ttm: TTM structure holding system pages.
  * @evicted: Whether the object was evicted without user-space knowing.
  * @cpu_writes: For synchronization. Number of cpu writers.
@@ -461,7 +461,7 @@
  * sleep interruptible.
  * @persistant_swap_storage: Usually the swap storage is deleted for buffers
  * pinned in physical memory. If this behaviour is not desired, this member
- * holds a pointer to a persistant shmem object. Typically, this would
+ * holds a pointer to a persistent shmem object. Typically, this would
  * point to the shmem object backing a GEM object if TTM is used to back a
  * GEM user interface.
  * @acc_size: Accounted size for this object.
@@ -508,7 +508,7 @@
  * sleep interruptible.
  * @persistant_swap_storage: Usually the swap storage is deleted for buffers
  * pinned in physical memory. If this behaviour is not desired, this member
- * holds a pointer to a persistant shmem object. Typically, this would
+ * holds a pointer to a persistent shmem object. Typically, this would
  * point to the shmem object backing a GEM object if TTM is used to back a
  * GEM user interface.
  * @p_bo: On successful completion *p_bo points to the created object.