tools: bpftool: close prog FD before exit on showing a single program

When showing metadata about a single program by invoking
"bpftool prog show PROG", the file descriptor referring to the program
is not closed before returning from the function. Let's close it.

Fixes: 71bb428 ("tools: bpf: add bpftool")
Signed-off-by: Quentin Monnet <quentin.monnet@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

tools/bpf/bpftool/prog.c

@@ -363,7 +363,9 @@ static int do_show(int argc, char **argv)
 		if (fd < 0)
 			return -1;
 
-		return show_prog(fd);
+		err = show_prog(fd);
+		close(fd);
+		return err;
 	}
 
 	if (argc)