dma-coherent: fix rmem_dma_device_init regression

My recent bug fix introduced another bug, which caused rmem_dma_device_init
to always fail, as rmem->priv is never set to anything.

This restores the previous behavior, calling dma_init_coherent_memory()
whenever ->priv is NULL.

Fixes: d35b0996fe ("dma-coherent: fix dma_declare_coherent_memory() logic error")
Reported-by: Roy Pledge <roy.pledge@nxp.com>
Tested-by: Roy Pledge <roy.pledge@nxp.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/base/dma-coherent.c

@@ -348,16 +348,15 @@ static int rmem_dma_device_init(struct reserved_mem *rmem, struct device *dev)
 	struct dma_coherent_mem *mem = rmem->priv;
 	int ret;
 
-	if (!mem)
-		return -ENODEV;
-
-	ret = dma_init_coherent_memory(rmem->base, rmem->base, rmem->size,
-				       DMA_MEMORY_EXCLUSIVE, &mem);
-
-	if (ret) {
-		pr_err("Reserved memory: failed to init DMA memory pool at %pa, size %ld MiB\n",
-			&rmem->base, (unsigned long)rmem->size / SZ_1M);
-		return ret;
+	if (!mem) {
+		ret = dma_init_coherent_memory(rmem->base, rmem->base,
+					       rmem->size,
+					       DMA_MEMORY_EXCLUSIVE, &mem);
+		if (ret) {
+			pr_err("Reserved memory: failed to init DMA memory pool at %pa, size %ld MiB\n",
+				&rmem->base, (unsigned long)rmem->size / SZ_1M);
+			return ret;
+		}
 	}
 	mem->use_dev_dma_pfn_offset = true;
 	rmem->priv = mem;