staging: ks7010: remove unused read_buf

Driver SDIO code allocates memory for a buffer that is never used. It
can be safely removed.

Remove unused buffer, including allocation and freeing of memory.

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