iwlwifi: mvm: prepare roc_done_wk to work sync

As part of changes made to properly support auxiliary activities in CDB
NICs, an aux sta will be added when using hot spot 2.0 and will need
to be removed when roc flow is done.
In order to do so, prepare the roc_done_wk to work synchronously as the
rm_aux_sta is a SYNC command.

Since now all of th iwl_mvm_flush_sta function are using it sync,
removed the flag argument from the function.

Signed-off-by: Nathan Errera <nathan.errera@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/iwlwifi.20201008180656.71b441c8b682.Ia1d216cb680308b91d6da9f73e23ae9f4baac79f@changeid