tools/libbpf: Avoid possibly using uninitialized variable

Fixes a GCC maybe-uninitialized warning introduced by 48cca7e4.
"text" is only initialized inside the if statement so only print debug
info there.

Fixes: 48cca7e4 ("libbpf: add support for bpf_call")
Signed-off-by: Jeremy Cline <jeremy@jcline.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>