iwlwifi: pcie: handle pcim_iomap_table() failures better

pcim_iomap_table() might return NULL, so we shouldn't unconditionally
dereference the return value by taking the [0] entry.

Handle this better by checking for NULL first, and then separately
checking if the [0] entry is NULL.
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20210612142637.9aa4f0e3574a.I458b283f203d5f927f00be1bfbd4b8ebf11c5ae4@changeidSigned-off-by: Luca Coelho <luciano.coelho@intel.com>

drivers/net/wireless/intel/iwlwifi/pcie/trans.c

@@ -3413,6 +3413,7 @@ struct iwl_trans *iwl_trans_pcie_alloc(struct pci_dev *pdev,
 	struct iwl_trans *trans;
 	int ret, addr_size;
 	const struct iwl_trans_ops *ops = &trans_ops_pcie_gen2;
+	void __iomem * const *table;
 
 	if (!cfg_trans->gen2)
 		ops = &trans_ops_pcie;
@@ -3485,9 +3486,16 @@ struct iwl_trans *iwl_trans_pcie_alloc(struct pci_dev *pdev,
 		goto out_no_pci;
 	}
 
-	trans_pcie->hw_base = pcim_iomap_table(pdev)[0];
-	if (!trans_pcie->hw_base) {
+	table = pcim_iomap_table(pdev);
+	if (!table) {
 		dev_err(&pdev->dev, "pcim_iomap_table failed\n");
+		ret = -ENOMEM;
+		goto out_no_pci;
+	}
+
+	trans_pcie->hw_base = table[0];
+	if (!trans_pcie->hw_base) {
+		dev_err(&pdev->dev, "couldn't find IO mem in first BAR\n");
 		ret = -ENODEV;
 		goto out_no_pci;
 	}