Merge branch 'libbpf: Fixed various checkpatch issues'

Kang Minchul says:

====================
This patch series contains various checkpatch fixes
in btf.c, libbpf.c, ringbuf.c.

I know these are trivial but some issues are hard to ignore
and I think these checkpatch issues are accumulating.

v1 -> v2: changed cover letter message.
====================

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>