drm/kmb: Remove an unnecessary NULL check

The NULL checking isn't done consistently in this function and it leads
to a static checker warning:

    drivers/gpu/drm/kmb/kmb_drv.c:561 kmb_pm_suspend()
    error: we previously assumed 'drm' could be null (see line 559)

Fortunately "drm" cannot be NULL at this point so the check can just be
removed.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Anitha Chrisanthus <anitha.chrisanthus@intel.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20201117072137.GB1111239@mwanda

drivers/gpu/drm/kmb/kmb_drv.c

@@ -556,7 +556,7 @@ MODULE_DEVICE_TABLE(of, kmb_of_match);
 static int __maybe_unused kmb_pm_suspend(struct device *dev)
 {
 	struct drm_device *drm = dev_get_drvdata(dev);
-	struct kmb_drm_private *kmb = drm ? to_kmb(drm) : NULL;
+	struct kmb_drm_private *kmb = to_kmb(drm);
 
 	drm_kms_helper_poll_disable(drm);