fpga: dfl: afu: remove set but not used variable 'afu'

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/fpga/dfl-afu-main.c: In function ‘afu_dev_destroy’:
drivers/fpga/dfl-afu-main.c:816:18: warning: variable ‘afu’
set but not used [-Wunused-but-set-variable]

It is never used, and so can be removed.
Acked-by: Wu Hao <hao.wu@intel.com>
Signed-off-by: yu kuai <yukuai3@huawei.com>
Signed-off-by: Moritz Fischer <mdf@kernel.org>

drivers/fpga/dfl-afu-main.c

@@ -813,10 +813,8 @@ static int afu_dev_init(struct platform_device *pdev)
 static int afu_dev_destroy(struct platform_device *pdev)
 {
 	struct dfl_feature_platform_data *pdata = dev_get_platdata(&pdev->dev);
-	struct dfl_afu *afu;
 
 	mutex_lock(&pdata->lock);
-	afu = dfl_fpga_pdata_get_private(pdata);
 	afu_mmio_region_destroy(pdata);
 	afu_dma_region_destroy(pdata);
 	dfl_fpga_pdata_set_private(pdata, NULL);