drm: fix spelling error in comments

Change the comment typo: "manger" -> "manager".
Signed-off-by: Wang Qing <wangqing@vivo.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/1600308275-32094-1-git-send-email-wangqing@vivo.com

include/drm/drm_mm.h

@@ -338,7 +338,7 @@ static inline u64 drm_mm_hole_node_end(const struct drm_mm_node *hole_node)
 
 /**
  * drm_mm_nodes - list of nodes under the drm_mm range manager
- * @mm: the struct drm_mm range manger
+ * @mm: the struct drm_mm range manager
  *
  * As the drm_mm range manager hides its node_list deep with its
  * structure, extracting it looks painful and repetitive. This is