drm: fix drmFreeDevices memory leak on multi GPU setups

When in multi GPU case, devices array may have some
NULL "hole" in between two devices. So check all
array elements and free non-NULL device.

Signed-off-by: Qiang Yu <Qiang.Yu@amd.com>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>

xf86drm.c

@@ -2993,7 +2993,8 @@ void drmFreeDevices(drmDevicePtr devices[], int count)
     if (devices == NULL)
         return;
 
-    for (i = 0; i < count && devices[i] != NULL; i++)
+    for (i = 0; i < count; i++)
+        if (devices[i])
             drmFreeDevice(&devices[i]);
 }