libbpf: Fix another potential overflow issue in bpf_prog_linfo

libbpf: Fix another potential overflow issue in bpf_prog_linfo

BugLink: https://bugs.launchpad.net/bugs/1861091
commit dd3ab126379ec040b3edab8559f9c72de6ef9d29 upstream.

Fix few issues found by Coverity and LGTM.

Fixes: b053b439b72a ("bpf: libbpf: bpftool: Print bpf_line_info during prog dump")
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20191107020855.3834758-4-andriin@fb.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>