iwlwifi: mvm: initialize iwl_dev_tx_power_cmd to zero

If the REDUCE_TX_POWER_CMD version is v4 or v5, we are not
initializing some values before sending to the FW, which causes SAR
not to work properly.  Solve this by initializing the struct in the
declaration.
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20200424194456.0dc957a264ff.I43cfd72d539c1287ccaaa454e95c673dac38214f@changeid

drivers/net/wireless/intel/iwlwifi/mvm/fw.c

@@ -787,13 +787,12 @@ int iwl_mvm_sar_select_profile(struct iwl_mvm *mvm, int prof_a, int prof_b)
 	union {
 		struct iwl_dev_tx_power_cmd v5;
 		struct iwl_dev_tx_power_cmd_v4 v4;
-	} cmd;
-
+	} cmd = {
+		.v5.v3.set_mode = cpu_to_le32(IWL_TX_POWER_MODE_SET_CHAINS),
+	};
 	int ret;
 	u16 len = 0;
 
-	cmd.v5.v3.set_mode = cpu_to_le32(IWL_TX_POWER_MODE_SET_CHAINS);
-
 	if (fw_has_api(&mvm->fw->ucode_capa,
 		       IWL_UCODE_TLV_API_REDUCE_TX_POWER))
 		len = sizeof(cmd.v5);