tools api io: Ensure line_len_out is always initialized

Ensure initialization to avoid compiler warnings about potential use
of uninitialized variables.

Signed-off-by: Ian Rogers <[e-mail]>
Cc: Ravi Bangoria <[e-mail]>
Cc: Yoshihiro Furudera <[e-mail]>
Cc: Howard Chu <[e-mail]>
Cc: Ze Gao <[e-mail]>
Cc: Changbin Du <[e-mail]>
Cc: Junhao He <[e-mail]>
Cc: Weilin Wang <[e-mail]>
Cc: James Clark <[e-mail]>
Cc: Oliver Upton <[e-mail]>
Cc: Athira Jajeev <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Namhyung Kim <[e-mail]>

tools/lib/api/io.h

···
 err_out:
 	free(line);
 	*line_out = NULL;
+	*line_len_out = 0;
 	return -ENOMEM;
 }