soundwire: intel: add missing headers for cross-compilation

readl/writel and ioread32 are used without the relevant headers, fix.

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20190916185739.32184-2-pierre-louis.bossart@linux.intel.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>
diff --git a/drivers/soundwire/intel.c b/drivers/soundwire/intel.c
index f1e38a2..bcc5077 100644
--- a/drivers/soundwire/intel.c
+++ b/drivers/soundwire/intel.c
@@ -10,6 +10,7 @@
 #include <linux/delay.h>
 #include <linux/module.h>
 #include <linux/interrupt.h>
+#include <linux/io.h>
 #include <linux/platform_device.h>
 #include <sound/pcm_params.h>
 #include <sound/soc.h>