Fix ignoring return value warning in WPEDisplayDRM::findDevice()

https://bugs.webkit.org/show_bug.cgi?id=268544

Reviewed by Carlos Garcia Campos.

The 273896@main introduces an wrong use of fd.release(). This
leads in a build warning error and a potential file descriptor leak.
Use 'fd = { };' instead of this to reset as invalid.

* Source/WebKit/WPEPlatform/wpe/drm/WPEDisplayDRM.cpp:
(findDevice):

Canonical link: https://commits.webkit.org/273902@main

Source/WebKit/WPEPlatform/wpe/drm/WPEDisplayDRM.cpp

@@ -95,7 +95,7 @@ static UnixFileDescriptor findDevice(GError** error)
         if (resources && resources->count_crtcs && resources->count_connectors && resources->count_encoders)
             break;
 
-        fd.release();
+        fd = { };
     }
 
     drmFreeDevices(devices, numDevices);