ath6kl: add Dell OEM SDIO I/O for the Venue 8 Pro

SDIO ID 0271:0418

Signed-off-by: Alan Cox <alan@linux.intel.com>
Bugzilla-ID: https://bugzilla.kernel.org/show_bug.cgi?id=67921


Reviewed-by: Steve deRosier <steve.derosier@lairdtech.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>