gpu: host1x: Check for valid host1x pointer

Under rare circumstances it can happen that the host1x driver's .probe()
doesn't finish properly, in which case the device's driver-specific data
will not be set. Instead of crashing in such a situation, propagate the
error to callers of the host1x_get_drm_data() function.

Signed-off-by: Thierry Reding <[e-mail]>

drivers/gpu/host1x/dev.c

···
 void *host1x_get_drm_data(struct device *dev)
 {
 	struct host1x *host1x = dev_get_drvdata(dev);
-	return host1x->drm_data;
+	return host1x ? host1x->drm_data : NULL;
 }
 
 void host1x_sync_writel(struct host1x *host1x, u32 v, u32 r)