Driver SDIO private data structure description includes a spin_lock
that is never used. This data structure only contains a pointer to the
sdio_func and a pointer to the main device private data. A spin_lock
is not required here.

Remove unused spin_lock.
Signed-off-by: Tobin C. Harding <me@tobin.cc>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>