ath11k: fix warning in ath11k_mhi_config

Initialize static variable ath11k_mhi_config for all hw_rev,
return error for unknown hw_rev.
This patch fixes below Smatch warning:
    drivers/net/wireless/ath/ath11k/mhi.c:357 ath11k_mhi_register()
    error: uninitialized symbol 'ath11k_mhi_config'.

Tested-on: QCN9074 hw1.0 PCI WLAN.HK.2.4.0.1-01734-QCAHKSWPL_SILICONZ-1

Fixes: a233811 ("ath11k: Add qcn9074 mhi controller config")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Anilkumar Kolli <akolli@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/1617857830-19315-1-git-send-email-akolli@codeaurora.org

drivers/net/wireless/ath/ath11k/mhi.c

@@ -349,10 +349,19 @@ int ath11k_mhi_register(struct ath11k_pci *ab_pci)
 	mhi_ctrl->read_reg = ath11k_mhi_op_read_reg;
 	mhi_ctrl->write_reg = ath11k_mhi_op_write_reg;
 
-	if (ab->hw_rev == ATH11K_HW_QCA6390_HW20)
-		ath11k_mhi_config = &ath11k_mhi_config_qca6390;
-	else if (ab->hw_rev == ATH11K_HW_QCN9074_HW10)
+	switch (ab->hw_rev) {
+	case ATH11K_HW_QCN9074_HW10:
 		ath11k_mhi_config = &ath11k_mhi_config_qcn9074;
+		break;
+	case ATH11K_HW_QCA6390_HW20:
+		ath11k_mhi_config = &ath11k_mhi_config_qca6390;
+		break;
+	default:
+		ath11k_err(ab, "failed assign mhi_config for unknown hw rev %d\n",
+			   ab->hw_rev);
+		mhi_free_controller(mhi_ctrl);
+		return -EINVAL;
+	}
 
 	ret = mhi_register_controller(mhi_ctrl, ath11k_mhi_config);
 	if (ret) {