clang-format: Use POSIX locale for `sort`

This avoids differences when different people run the command,
which is relevant for our use case, e.g.:

    $ LC_ALL=en_US.UTF-8 sort test
    ata_for_each_link
    __ata_qc_for_each
    ata_qc_for_each

    $ LC_ALL=C sort test
    __ata_qc_for_each
    ata_for_each_link
    ata_qc_for_each

Link: https://lore.kernel.org/lkml/CANiq72=7=ZpAObWRmposOmnyZ8XR_eNHCBtA3bu3fusmcPUwDA@mail.gmail.com/


Signed-off-by: Miguel Ojeda <ojeda@kernel.org>