tools: bpftool: fix arguments for p_err() in do_event_pipe()

The last argument passed to some calls to the p_err() functions is not
correct, it should be "*argv" instead of "**argv". This may lead to a
segmentation fault error if CPU IDs or indices from the command line
cannot be parsed correctly. Let's fix this.

Fixes: f412eed9

 ("tools: bpftool: add simple perf event output reader")
Signed-off-by: Quentin Monnet <quentin.monnet@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>