iwlwifi: dbg-tlv: fix old length in is_trig_data_contained()

There's a bug in the lengths - the 'old length' needs to be calculated
using the 'old' pointer, of course, likely a copy/paste mistake. Fix
this.

Reported-by: Daniel Gabay <daniel.gabay@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Fixes: cf29c5b6 ("iwlwifi: dbg_ini: implement time point handling")
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20201209231352.c0105ddffa74.I1ddb243053ff763c91b663748b6a593ecc3b5634@changeid


Signed-off-by: Luca Coelho <luciano.coelho@intel.com>