selftests/bpf: Fix mix of tabs and spaces

Clang's -Wmisleading-indentation warns about misleading indentations if
there's a mixture of spaces and tabs. Remove extraneous spaces.

Signed-off-by: Bill Wendling <morbo@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20200320201510.217169-1-morbo@google.com