SDIO header file does not use kernel doc format struct
comments. Adding them aids readability and enables documentation to be
built from the source code. Other comments may be tidied up as we do this.

Add kernel format struct comments. Tidy up comments.
Signed-off-by: Tobin C. Harding <me@tobin.cc>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>