update sysfw version path for compatibility with new bios updater

The new BIOS updater[1] reads and writes the BIOS version from
/var/bios/host0_bios_version.txt. This change updates the version
path from /var/lib/fb-ipmi-oem/appData.json to
/var/bios/host0_bios_version.txt to ensure compatibility and allow the
new updater to retrieve the BIOS version correctly.

[1] https://gerrit.openbmc.org/c/openbmc/phosphor-bmc-code-mgmt/+/76101

Tested on Harma:
```
curl --silent $creds https://$bmc/redfish/v1/UpdateService/FirmwareInventory/Harma_BIOS_7246
{
  "@odata.id": "/redfish/v1/UpdateService/FirmwareInventory/Harma_BIOS_7246",
  "@odata.type": "#SoftwareInventory.v1_1_0.SoftwareInventory",
  "Description": "Unknown image",
  "Id": "Harma_BIOS_7246",
  "Name": "Software Inventory",
  "Status": {
    "Health": "Warning",
    "HealthRollup": "OK",
    "State": "Disabled"
  },
  "Updateable": true,
  "Version": "F0M_2A08"
}
```

Signed-off-by: Kevin Tung <Kevin.Tung@quantatw.com>
Change-Id: If19b4b006961cd7514ac9556dfbf34845b7c1b74
diff --git a/src/usb-dbg.cpp b/src/usb-dbg.cpp
index 4e2847d..d125016 100644
--- a/src/usb-dbg.cpp
+++ b/src/usb-dbg.cpp
@@ -528,23 +528,20 @@
 
 static int getBiosVer(std::string& ver, size_t hostPosition)
 {
-    nlohmann::json appObj;
-
-    std::ifstream file(JSON_APP_DATA_FILE);
-    if (file)
+    std::string sysfwVersionFile = std::format(SYSFW_VER_FILE, hostPosition);
+    std::ifstream file(sysfwVersionFile);
+    if (!file)
     {
-        file >> appObj;
-        file.close();
-        std::string version_key = KEY_SYSFW_VER + std::to_string(hostPosition);
-
-        if (appObj.find(version_key) != appObj.end())
-        {
-            ver = appObj[version_key].get<std::string>();
-            return 0;
-        }
+        phosphor::logging::log<phosphor::logging::level::ERR>(
+            "Failed to open system firmware version file",
+            phosphor::logging::entry("FILE=%s", sysfwVersionFile.c_str()));
+        return -1;
     }
 
-    return -1;
+    std::getline(file, ver);
+    file.close();
+
+    return 0;
 }
 
 int sendBicCmd(uint8_t netFn, uint8_t cmd, uint8_t bicAddr,