media: v4l2-ctrls-core.c: Do not use iterator outside loop

Simplify a bit the code introducing a new variable for iterating through
the control list.

It also makes smatch happy:

drivers/media/v4l2-core/v4l2-ctrls-api.c:1091 v4l2_query_ext_ctrl() warn: iterator used outside loop: 'ref'
Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
[hverkuil: fix tiny whitespace issue in 'pos  = ref': use just one space]

drivers/media/v4l2-core/v4l2-ctrls-api.c

@@ -1052,35 +1052,40 @@ int v4l2_query_ext_ctrl(struct v4l2_ctrl_handler *hdl, struct v4l2_query_ext_ctr
 		if (id >= node2id(hdl->ctrl_refs.prev)) {
 			ref = NULL; /* Yes, so there is no next control */
 		} else if (ref) {
+			struct v4l2_ctrl_ref *pos = ref;
+
 			/*
 			 * We found a control with the given ID, so just get
 			 * the next valid one in the list.
 			 */
-			list_for_each_entry_continue(ref, &hdl->ctrl_refs, node) {
-				is_compound = ref->ctrl->is_array ||
-					ref->ctrl->type >= V4L2_CTRL_COMPOUND_TYPES;
-				if (id < ref->ctrl->id &&
-				    (is_compound & mask) == match)
+			ref = NULL;
+			list_for_each_entry_continue(pos, &hdl->ctrl_refs, node) {
+				is_compound = pos->ctrl->is_array ||
+					pos->ctrl->type >= V4L2_CTRL_COMPOUND_TYPES;
+				if (id < pos->ctrl->id &&
+				    (is_compound & mask) == match) {
+					ref = pos;
 					break;
+				}
 			}
-			if (&ref->node == &hdl->ctrl_refs)
-				ref = NULL;
 		} else {
+			struct v4l2_ctrl_ref *pos;
+
 			/*
 			 * No control with the given ID exists, so start
 			 * searching for the next largest ID. We know there
 			 * is one, otherwise the first 'if' above would have
 			 * been true.
 			 */
-			list_for_each_entry(ref, &hdl->ctrl_refs, node) {
-				is_compound = ref->ctrl->is_array ||
-					ref->ctrl->type >= V4L2_CTRL_COMPOUND_TYPES;
-				if (id < ref->ctrl->id &&
-				    (is_compound & mask) == match)
+			list_for_each_entry(pos, &hdl->ctrl_refs, node) {
+				is_compound = pos->ctrl->is_array ||
+					pos->ctrl->type >= V4L2_CTRL_COMPOUND_TYPES;
+				if (id < pos->ctrl->id &&
+				    (is_compound & mask) == match) {
+					ref = pos;
 					break;
+				}
 			}
-			if (&ref->node == &hdl->ctrl_refs)
-				ref = NULL;
 		}
 	}
 	mutex_unlock(hdl->lock);