soundwire: cdns: Fix compilation error on arm64

On arm64 the cadence_master.c file doesn't compile.

readl and writel are undefined.
This patch fixes that by including io.h.

Signed-off-by: Jan Kotas <jank@cadence.com>
Reviewed-by: Mukesh Ojha <mojha@codeaurora.org>
Signed-off-by: Vinod Koul <vkoul@kernel.org>