drm/kms-helpers: Use recommened kerneldoc for struct member refs

I just learned that &struct_name.member_name works and looks pretty
even. It doesn't (yet) link to the member directly though, which would
be really good for big structures or vfunc tables (where the
per-member kerneldoc tends to be long).

Also some minor drive-by polish where it makes sense, I read a lot
of docs ...

v2: Comments from Gustavo.

Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Rewiewed-by: Gustavo Padovan <gustavo.padovan@collabora.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170125062657.19270-2-daniel.vetter@ffwll.ch

drivers/gpu/drm/drm_dp_helper.c

@@ -725,7 +725,7 @@ MODULE_PARM_DESC(dp_aux_i2c_speed_khz,
 /*
  * Transfer a single I2C-over-AUX message and handle various error conditions,
  * retrying the transaction as appropriate.  It is assumed that the
- * aux->transfer function does not modify anything in the msg other than the
+ * &drm_dp_aux.transfer function does not modify anything in the msg other than the
  * reply field.
  *
  * Returns bytes transferred on success, or a negative error code on failure.