mei: constify buffer in the write functions calls

The write buffer should not by modified so make it constant. Also
hitchhike some style fixes on the way in the interface and rename
mei_me_write_message to mei_me_hbuf_write for consistency.

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/misc/mei/mei_dev.h

@@ -300,10 +300,9 @@ struct mei_hw_ops {
 	int (*hbuf_free_slots)(struct mei_device *dev);
 	bool (*hbuf_is_ready)(struct mei_device *dev);
 	size_t (*hbuf_max_len)(const struct mei_device *dev);
-
 	int (*write)(struct mei_device *dev,
 		     struct mei_msg_hdr *hdr,
-		     unsigned char *buf);
+		     const unsigned char *buf);
 
 	int (*rdbuf_full_slots)(struct mei_device *dev);
 
@@ -665,7 +664,7 @@ static inline size_t mei_hbuf_max_len(const struct mei_device *dev)
 }
 
 static inline int mei_write_message(struct mei_device *dev,
-			struct mei_msg_hdr *hdr, void *buf)
+				    struct mei_msg_hdr *hdr, const void *buf)
 {
 	return dev->ops->write(dev, hdr, buf);
 }