RVV: add missing SPDX-License-Identifier to PacketMathDecl.h

libeigen/eigen!2514

Co-authored-by: Rasmus Munk Larsen <rmlarsen@gmail.com>

Eigen/src/Core/arch/RVV10/PacketMathDecl.h

diff --git a/Eigen/src/Core/arch/RVV10/PacketMathDecl.h b/Eigen/src/Core/arch/RVV10/PacketMathDecl.h
index 9f745c8..a3ab51b 100644
--- a/Eigen/src/Core/arch/RVV10/PacketMathDecl.h
+++ b/Eigen/src/Core/arch/RVV10/PacketMathDecl.h
@@ -7,6 +7,7 @@
 // This Source Code Form is subject to the terms of the Mozilla
 // Public License v. 2.0. If a copy of the MPL was not distributed
 // with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
+// SPDX-License-Identifier: MPL-2.0
 
 #ifndef EIGEN_PACKET_MATH_RVV10_DECL_H
 #define EIGEN_PACKET_MATH_RVV10_DECL_H