mfd: cros_ec: Allow static din/dout buffers with cros_ec_register()

The lower-level driver may want to provide its own buffers. If so,
there's no need to allocate new ones.  This already happens to work
just fine (since we check for size of 0 and use devm allocation), but
it's good to document it.

[dianders: Resolved conflicts; documented that no code changes needed
on mainline]

Signed-off-by: Bill Richardson <wfrichar@chromium.org>
Signed-off-by: Doug Anderson <dianders@chromium.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

include/linux/mfd/cros_ec.h

@@ -68,8 +68,8 @@ struct cros_ec_msg {
  * We use this alignment to keep ARM and x86 happy. Probably word
  * alignment would be OK, there might be a small performance advantage
  * to using dword.
- * @din_size: size of din buffer
- * @dout_size: size of dout buffer
+ * @din_size: size of din buffer to allocate (zero to use static din)
+ * @dout_size: size of dout buffer to allocate (zero to use static dout)
  * @command_send: send a command
  * @command_recv: receive a command
  * @ec_name: name of EC device (e.g. 'chromeos-ec')