ftbfs in focal

[Matthias Klose]

seen in the second focal test rebuild
https://launchpadlibrarian.net/471195717/buildlog_ubuntu-focal-amd64.linux-restricted-modules-oem-5.4_5.4.0-1002.4_BUILDING.txt.gz

II: dkms-build installing nvidia-390 into /<<PKGBUILDDIR>>/debian/linux-modules-nvidia-390-5.4.0-1002-oem/lib/modules/5.4.0-1002-oem/kernel/nvidia-390
copying nvidia-uvm.ko
copying nvidia.ko
copying nvidia-drm.ko
copying nvidia-modeset.ko
II: dkms-build override dkms-build--nvidia-N found, executing
II: checking gcc version ...
GCC: (Ubuntu 9.2.1-23ubuntu2) 9.2.1 20200110
gcc (Ubuntu 9.3.0-8ubuntu1) 9.3.0
Copyright (C) 2019 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

WW: gcc version missmatch between linux and linux-restricted-modules
WW: was: gcc (Ubuntu 9.2.1-23ubuntu2) 9.2.1 20200110 is: gcc (Ubuntu 9.3.0-8ubuntu1) 9.3.0
II: adding signatures from /usr/lib/linux/5.4.0-1002-oem ...
nvidia-drm.ko: FAILED
nvidia-modeset.ko: FAILED
nvidia-uvm.ko: FAILED
nvidia.ko: FAILED
sha256sum: WARNING: 4 computed checksums did NOT match
make[1]: *** [debian/rules:129: nvidia-oem] Error 1
make[1]: Leaving directory '/<<PKGBUILDDIR>>'
make: *** [debian/rules:82: binary] Error 2