mfd: wm8400-core: Supply description for wm8400_reset_codec_reg_cache's arg

Kerneldoc syntax is used, but not complete. Descriptions required.

Prevents warnings like:

drivers/mfd/wm8400-core.c:113: warning: Function parameter or member 'wm8400' not described in 'wm8400_reset_codec_reg_cache'

Cc: Mark Brown <[e-mail]>
Cc: [e-mail]
Signed-off-by: Lee Jones <[e-mail]>
Acked-by: Charles Keepax <[e-mail]>
Signed-off-by: Lee Jones <[e-mail]>

drivers/mfd/wm8400-core.c

···
 /**
  * wm8400_reset_codec_reg_cache - Reset cached codec registers to
  * their default values.
+ *
+ * @wm8400: pointer to local driver data structure
  */
 void wm8400_reset_codec_reg_cache(struct wm8400 *wm8400)
 {