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_framebuffer.c b/drivers/gpu/drm/drm_framebuffer.c
index 7abcb26..d8d75e2 100644
--- a/drivers/gpu/drm/drm_framebuffer.c
+++ b/drivers/gpu/drm/drm_framebuffer.c
@@ -773,7 +773,7 @@ EXPORT_SYMBOL(drm_framebuffer_lookup);
  * @fb: fb to unregister
  *
  * Drivers need to call this when cleaning up driver-private framebuffers, e.g.
- * those used for fbdev. Note that the caller must hold a reference of it's own,
+ * those used for fbdev. Note that the caller must hold a reference of its own,
  * i.e. the object may not be destroyed through this call (since it'll lead to a
  * locking inversion).
  *