xf86drm: cap number of reported devices by drmGetDevice(2)

Do as the documentation says - cap the number of reported devices to the
requested amount - aka max_devices. Otherwise we risk out-of-bound access
for users of the API.

Issue: https://gitlab.freedesktop.org/mesa/drm/-/issues/56
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Simon Ser <contact@emersion.fr>

xf86drm.c

@@ -4263,12 +4263,13 @@ drm_public int drmGetDevices2(uint32_t flags, drmDevicePtr devices[],
         if (!local_devices[i])
             continue;
 
-        if ((devices != NULL) && (device_count < max_devices))
+        if ((devices != NULL) && (device_count < max_devices)) {
             devices[device_count] = local_devices[i];
-        else
-            drmFreeDevice(&local_devices[i]);
-
             device_count++;
+        } else {
+            drmFreeDevice(&local_devices[i]);
+        }
+
     }
 
     closedir(sysdir);