mtd: nand: omap2: Don't call dma_release_channel() if dma_request_chan() failed

dma_request_chan() can fail returning an error pointer. In this case
prevent calling dma_release_channel() to prevent a ERR_PTR() dereference.

As error path can be called even with no DMA configuration, info->dma can
be NULL so don't call dma_release_channel() for that case either.

Fixes: de3bfc4a1616: ("mtd: nand: omap2: fix return value check in omap_nand_probe()")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Roger Quadros <rogerq@ti.com>
Acked-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>

drivers/mtd/nand/omap2.c

@@ -2169,7 +2169,7 @@ scan_tail:
 	return 0;
 
 return_error:
-	if (info->dma)
+	if (!IS_ERR_OR_NULL(info->dma))
 		dma_release_channel(info->dma);
 	if (nand_chip->ecc.priv) {
 		nand_bch_free(nand_chip->ecc.priv);