pipe: remove KM_USER0 from comments

Signed-off-by: Cong Wang <amwang@redhat.com>
diff --git a/fs/pipe.c b/fs/pipe.c
index 49c1065..95cbd6b 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -224,7 +224,7 @@
  *	and the caller has to be careful not to fault before calling
  *	the unmap function.
  *
- *	Note that this function occupies KM_USER0 if @atomic != 0.
+ *	Note that this function calls kmap_atomic() if @atomic != 0.
  */
 void *generic_pipe_buf_map(struct pipe_inode_info *pipe,
 			   struct pipe_buffer *buf, int atomic)