mei: add mei_hbuf_acquire wrapper

A client has to acquire host buffer
before writing, we add lock like wrapper
to replace the code snippet

if (dev->hbuf_is_ready)
        dev->hbuf_is_ready = false;

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/misc/mei/interrupt.c b/drivers/misc/mei/interrupt.c
index 6c4597e..aed03ef 100644
--- a/drivers/misc/mei/interrupt.c
+++ b/drivers/misc/mei/interrupt.c
@@ -446,10 +446,10 @@
 	s32 slots;
 	int ret;
 
-	if (!mei_hbuf_is_ready(dev)) {
-		dev_dbg(&dev->pdev->dev, "host buffer is not empty.\n");
+
+	if (!mei_hbuf_acquire(dev))
 		return 0;
-	}
+
 	slots = mei_hbuf_empty_slots(dev);
 	if (slots <= 0)
 		return -EMSGSIZE;