iwlwifi: mvm: initialize the cur_ucode upon boot

mvm->cur_ucode wasn't set before we actually load the
firmware. This caused issues when we boot in RFKILL since
we get an RFKILL interrupt upon boot even before we load
any firmware.
This leads to issues since iwl_mvm_set_hw_rfkill_state
(the RFKILL interrupts handler in mvm) relies on this
variable.

Fix this.

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>