mei: Add include of <linux/irqreturn.h>

We currently include <linux/irqreturn.h> in <linux/pci.h>, but I'm about to
remove that from linux/pci.h, so add explicit includes where needed.
Signed-off-by: NBjorn Helgaas <bhelgaas@google.com>
Acked-by: NTomas Winkler <tomas.winkler@intel.com>

drivers/misc/mei/hw-me.h

@@ -20,6 +20,7 @@
 #define _MEI_INTERFACE_H_
 
 #include <linux/mei.h>
+#include <linux/irqreturn.h>
 #include "mei_dev.h"
 #include "client.h"