avformat/mxfenc: Move sponsorship notice to its own comment block

Suggested-by: BBB
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/mxfenc.c

@@ -18,7 +18,9 @@
  * You should have received a copy of the GNU Lesser General Public
  * License along with FFmpeg; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
- *
+ */
+
+/*
  * signal_standard, color_siting and klv_fill_key version fixes sponsored by NOA GmbH
  */