system: squash usb_parse into a single function

We don't need to wrap usb_device_add as usb_parse is already gated
with an if (machine_usb(current_machine)) check. Instead just assert
and directly fail if usbdevice_create returns NULL.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20250116160306.1709518-10-alex.bennee@linaro.org>

system/vl.c

@@ -811,31 +811,17 @@ static void configure_msg(QemuOpts *opts)
 /***********************************************************/
 /* USB devices */
 
-static int usb_device_add(const char *devname)
+static int usb_parse(const char *cmdline)
 {
-    USBDevice *dev = NULL;
+    g_assert(machine_usb(current_machine));
 
-    if (!machine_usb(current_machine)) {
+    if (!usbdevice_create(cmdline)) {
+        error_report("could not add USB device '%s'", cmdline);
         return -1;
     }
-
-    dev = usbdevice_create(devname);
-    if (!dev)
-        return -1;
-
     return 0;
 }
 
-static int usb_parse(const char *cmdline)
-{
-    int r;
-    r = usb_device_add(cmdline);
-    if (r < 0) {
-        error_report("could not add USB device '%s'", cmdline);
-    }
-    return r;
-}
-
 /***********************************************************/
 /* machine registration */