iwlwifi: mvm: fix imbalanced locking in iwl_mvm_start_get_nvm()

If iwl_transt_start_hw() failed, we were returning without calling
wiphy_unlock() and rtnl_unlock(), causing a locking imbalance:

drivers/net/wireless/intel/iwlwifi/mvm/ops.c:686:12: warning: context imbalance in 'iwl_mvm_start_get_nvm' - wrong count at exit

Fix that by adding the unlock calls.

Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20211219090128.42417-2-luca@coelho.fi