dmaengine: qcom_hidma: avoid freeing an uninitialized pointer

If device_node np doesn't contain child or first child doesn't have
property "reg" then hidma_mgmt_of_populate_channels() perfoms
deallocation on uninitialized local variable res.

The patch adds res initialization by NULL.

Found by Linux Driver Verification project (linuxtesting.org).
Signed-off-by: Anton Vasilyev <vasilyev@ispras.ru>
Reviewed-by: Sinan Kaya <okaya@codeaurora.org>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

drivers/dma/qcom/hidma_mgmt.c

@@ -358,7 +358,7 @@ static int __init hidma_mgmt_of_populate_channels(struct device_node *np)
 	struct platform_device_info pdevinfo;
 	struct of_phandle_args out_irq;
 	struct device_node *child;
-	struct resource *res;
+	struct resource *res = NULL;
 	const __be32 *cell;
 	int ret = 0, size, i, num;
 	u64 addr, addr_size;