libbpf: Fix comment typo

Remove the repeated word 'the' in line 48.

Signed-off-by: Jason Wang <wangborong@cdjrlc.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20210727115928.74600-1-wangborong@cdjrlc.com