iwlwifi: mvm: initialize gtkdata->mvm correctly

gtkdata->mvm wasn't set in iwl_mvm_d0i3_update_keys,
resulting in kernel panic in some flows (when mvm
is actually used...)

Fixes: a3f7ba5c ("iwlwifi: update key params on d0i3 entrance/exit")
Signed-off-by: Eliad Peller <eliadx.peller@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>