v4l2bufferpool: Explicitly cast enum "subtype" to its "supertype"

gstv4l2bufferpool.c:608:18: error: implicit conversion from enumeration type
      'enum _GstV4l2BufferPoolAcquireFlags' to different enumeration type
      'GstBufferPoolAcquireFlags' [-Werror,-Wenum-conversion]
  params.flags = GST_V4L2_POOL_ACQUIRE_FLAG_RESURECT;
               ~ ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

sys/v4l2/gstv4l2bufferpool.c

@@ -605,9 +605,10 @@ gst_v4l2_buffer_pool_group_released (GstV4l2BufferPool * pool)
 
   GST_DEBUG_OBJECT (pool, "A buffer was lost, reallocating it");
 
-  params.flags = GST_V4L2_POOL_ACQUIRE_FLAG_RESURECT;
-  ret = gst_buffer_pool_acquire_buffer (GST_BUFFER_POOL (pool), &buffer,
-      &params);
+  params.flags =
+      (GstBufferPoolAcquireFlags) GST_V4L2_POOL_ACQUIRE_FLAG_RESURECT;
+  ret =
+      gst_buffer_pool_acquire_buffer (GST_BUFFER_POOL (pool), &buffer, &params);
 
   if (ret == GST_FLOW_OK)
     gst_buffer_unref (buffer);