drm/imagination: Use memdup_user() helper

Switching to memdup_user(), which combines kmalloc() and copy_from_user(),
and it can simplfy code.

Signed-off-by: Jinjie Ruan <[e-mail]>
Suggested-by: Christophe JAILLET <[e-mail]>
Reviewed-by: Frank Binns <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]
Signed-off-by: Matt Coster <[e-mail]>

drivers/gpu/drm/imagination/pvr_context.c

···
 	void *stream;
 	int err;
 
-	stream = kzalloc(stream_size, GFP_KERNEL);
-	if (!stream)
-		return -ENOMEM;
-
-	if (copy_from_user(stream, u64_to_user_ptr(stream_user_ptr), stream_size)) {
-		err = -EFAULT;
-		goto err_free;
-	}
+	stream = memdup_user(u64_to_user_ptr(stream_user_ptr), stream_size);
+	if (IS_ERR(stream))
+		return PTR_ERR(stream);
 
 	err = pvr_stream_process(pvr_dev, cmd_defs, stream, stream_size, dest);
-	if (err)
-		goto err_free;
 
-	kfree(stream);
-
-	return 0;
-
-err_free:
 	kfree(stream);
 
 	return err;