avfvideosrc: fix wrong framerate selected for caps

This fix solves an issue where a format that doesn't support the
requested framerate would be selected. It ensures that we use the first
format and framerate pair that supports the requested caps.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/2331>

subprojects/gst-plugins-bad/sys/applemedia/avfvideosrc.m

@@ -671,6 +671,10 @@ checked:
             break;
           }
         }
+
+        if (found_framerate) {
+          break;
+        }
       }
     }
     if (!found_format) {