Update license field to SPDX identifier

PKGBUILD

@@ -8,7 +8,7 @@ pkgrel=2
 pkgdesc="NVIDIA's GPU programming toolkit"
 arch=('x86_64')
 url="https://developer.nvidia.com/cuda-zone"
-license=('custom:NVIDIA')
+license=(LicenseRef-NVIDIA-CUDA)
 depends=('opencl-nvidia' 'nvidia-utils' 'python' 'gcc12')
 options=(!strip staticlibs)
 install=cuda.install