drm: Trivial comment grammar cleanups

Most of these are just cases where code comments used contractions
(it's, who's) where they actually mean to use a possessive pronoun (its,
whose) or vice-versa.

Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20190202012326.20096-1-matthew.d.roper@intel.com
diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
index 2896ff6..d0b9f6a 100644
--- a/drivers/gpu/drm/drm_gem.c
+++ b/drivers/gpu/drm/drm_gem.c
@@ -660,7 +660,7 @@ void drm_gem_put_pages(struct drm_gem_object *obj, struct page **pages,
 EXPORT_SYMBOL(drm_gem_put_pages);
 
 /**
- * drm_gem_object_lookup - look up a GEM object from it's handle
+ * drm_gem_object_lookup - look up a GEM object from its handle
  * @filp: DRM file private date
  * @handle: userspace handle
  *