dma-buf: minor doc touch-ups

Just some tiny edits:
- fix link to struct dma_fence
- give slightly more meaningful title - the polling here is about
  implicit fences, explicit fences (in sync_file or drm_syncobj) also
  have their own polling

v2: I misplaced the .rst include change corresponding to this patch.
Reviewed-by: Thomas Hellstrom <thomas.hellstrom@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200612070535.1778368-1-daniel.vetter@ffwll.ch

Documentation/driver-api/dma-buf.rst

@@ -100,11 +100,11 @@ CPU Access to DMA Buffer Objects
 .. kernel-doc:: drivers/dma-buf/dma-buf.c
    :doc: cpu access
 
-Fence Poll Support
-~~~~~~~~~~~~~~~~~~
+Implicit Fence Poll Support
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 .. kernel-doc:: drivers/dma-buf/dma-buf.c
-   :doc: fence polling
+   :doc: implicit fence polling
 
 Kernel Functions and Structures Reference
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

drivers/dma-buf/dma-buf.c

@@ -161,11 +161,11 @@ static loff_t dma_buf_llseek(struct file *file, loff_t offset, int whence)
 }
 
 /**
- * DOC: fence polling
+ * DOC: implicit fence polling
  *
  * To support cross-device and cross-driver synchronization of buffer access
- * implicit fences (represented internally in the kernel with &struct fence) can
- * be attached to a &dma_buf. The glue for that and a few related things are
+ * implicit fences (represented internally in the kernel with &struct dma_fence)
+ * can be attached to a &dma_buf. The glue for that and a few related things are
  * provided in the &dma_resv structure.
  *
  * Userspace can query the state of these implicitly tracked fences using poll()