fpga: dfl: make uinit callback optional

This patch makes uinit callback of sub features optional. With
this change, people don't need to prepare any empty uinit callback.

Signed-off-by: Wu Hao <hao.wu@intel.com>
Link: https://lore.kernel.org/r/1564914022-3710-9-git-send-email-hao.wu@intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/fpga/dfl.c

@@ -259,6 +259,7 @@ void dfl_fpga_dev_feature_uinit(struct platform_device *pdev)
 
 	dfl_fpga_dev_for_each_feature(pdata, feature)
 		if (feature->ops) {
+			if (feature->ops->uinit)
 				feature->ops->uinit(pdev, feature);
 			feature->ops = NULL;
 		}