Staging: rtl8192u - changed include of asm/io.h

Changed include of <asm/io.h> to be <linux/io.h>
Complies, but I don't have hardware.
Found using checkpatch.

Signed-off-by: Derek Robson <robsonde@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>