lib/op: fix small leak in op_hdr_u64_val_lookup
lib/op: fix small leak in op_hdr_u64_val_lookup

Free the corresponding u64 string.

Signed-off-by: David Disseldorp <589a549dc9f982d9f46aeeb82a09ab6d87ccf1d8@suse.de>

ddiss/elasto,ddiss/elasto