gpu:drm: Fix typo in Documentation/DocBook/drm.xml

This patch fix spelling typos found in drm.xml.
It is because the file is generated from comments in
source codes, I have to fix the typos within source files.

Signed-off-by: Masanari Iida <standby24x7@gmail.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/include/drm/drm_dp_mst_helper.h b/include/drm/drm_dp_mst_helper.h
index 9b446ad..3ecfcc1 100644
--- a/include/drm/drm_dp_mst_helper.h
+++ b/include/drm/drm_dp_mst_helper.h
@@ -28,7 +28,7 @@
 struct drm_dp_mst_branch;
 
 /**
- * struct drm_dp_vcpi - Virtual Channel Payload Identifer
+ * struct drm_dp_vcpi - Virtual Channel Payload Identifier
  * @vcpi: Virtual channel ID.
  * @pbn: Payload Bandwidth Number for this channel
  * @aligned_pbn: PBN aligned with slot size