staging: ccree: document spinlock usage

Document spinlock usage to protect against concurrent
access to HW register which must occur a single
request at a time.
Signed-off-by: Gilad Ben-Yossef <gilad@benyossef.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/ccree/ssi_request_mgr.c

@@ -43,6 +43,9 @@ struct ssi_request_mgr_handle {
 	u32 req_queue_tail;
 	u32 axi_completed;
 	u32 q_free_slots;
+	/* This lock protects access to HW register
+	 * that must be single request at a time
+	 */
 	spinlock_t hw_lock;
 	struct cc_hw_desc compl_desc;
 	u8 *dummy_comp_buff;