staging: omap-thermal: fix compilation

Because we are not including linux/io.h, the driver is not compiling.
This patch adds the missing header.
Signed-off-by: NEduardo Valentin <eduardo.valentin@ti.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/omap-thermal/omap-bandgap.c

@@ -38,6 +38,7 @@
 #include <linux/of_device.h>
 #include <linux/of_platform.h>
 #include <linux/of_irq.h>
+#include <linux/io.h>
 
 #include "omap-bandgap.h"