staging: unisys: add comment to spinlock in struct charqueue

Add a comment to the charqueue's spinlock to explain that it is a lock for the
structure.
Signed-off-by: Ken Depro <kenneth.depro@unisys.com>
Signed-off-by: Benjamin Romer <benjamin.romer@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/unisys/visorutil/charqueue.c

@@ -28,7 +28,7 @@
 struct charqueue {
 	int alloc_size;
 	int nslots;
-	spinlock_t lock;
+	spinlock_t lock; /* read/write lock for this structure */
 	int head, tail;
 	unsigned char buf[0];
 };