iwlwifi: mvm: d3: missing unlock in iwl_mvm_wowlan_program_keys()

This code was refactored and the mutex_unlock(&mvm->mutex); was
accidentally deleted.

Fixes: af3aab9c ("iwlwifi: mvm: d3: make key reprogramming iteration optional")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Luca Coelho <luca@coelho.fi>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210831081849.GB9846@kili