selftests: drv-net: devmem: remove sudo from system() calls

selftests: drv-net: devmem: remove sudo from system() calls

The general expectations for network HW selftests is that they
will be run as root. sudo doesn't seem to work on NIPA VMs.
While it's probably something solvable in the setup I think we should
remove the sudos. devmem is the only networking test using sudo.

Reviewed-by: Joe Damato <joe@dama.to>
Reviewed-by: Mina Almasry <almasrymina@google.com>
Acked-by: Stanislav Fomichev <sdf@fomichev.me>
Link: https://patch.msgid.link/20250811231334.561137-3-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>