fpga: Fix dead store fpga-mgr.c

Using clang's scan-build/view this issue was flagged in fpga-mgr.c

  drivers/fpga/fpga-mgr.c:585:3: warning: Value stored to 'ret' is never read [deadcode.DeadStores]
                  ret = id;
Signed-off-by: Tom Rix <trix@redhat.com>
Signed-off-by: Moritz Fischer <mdf@kernel.org>

drivers/fpga/fpga-mgr.c

@@ -581,10 +581,8 @@ struct fpga_manager *fpga_mgr_create(struct device *dev, const char *name,
 		return NULL;
 
 	id = ida_simple_get(&fpga_mgr_ida, 0, 0, GFP_KERNEL);
-	if (id < 0) {
-		ret = id;
+	if (id < 0)
 		goto error_kfree;
-	}
 
 	mutex_init(&mgr->ref_mutex);