Merge branch 'libbpf: fix several issues reported by static analysers'

Viktor Malik says:

====================

Fixing several issues reported by Coverity and Clang Static Analyzer
(scan-build) for libbpf, mostly removing unnecessary symbols and
assignments.

No functional changes should be introduced.
====================

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