mtd/omap2: fix dmaengine_slave_config error handling

The newly added dmaengine support in the omap2 nand driver
potentially causes an undefined return value from the
omap_nand_probe function when dmaengine_slave_config
reports an error. Let's handle this by returning the
same error back to the caller.

Without this patch, building omap2plus_defconfig results in:

drivers/mtd/nand/omap2.c: In function 'omap_nand_probe':
drivers/mtd/nand/omap2.c:1154:6: warning: 'err' may be used uninitialized in this function [-Wuninitialized]
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Russell King <rmk+kernel@arm.linux.org.uk>
Cc: Grazvydas Ignotas <notasas@gmail.com>

drivers/mtd/nand/omap2.c

@@ -1245,7 +1245,6 @@ static int __devinit omap_nand_probe(struct platform_device *pdev)
 			goto out_release_mem_region;
 		} else {
 			struct dma_slave_config cfg;
-			int rc;
 
 			memset(&cfg, 0, sizeof(cfg));
 			cfg.src_addr = info->phys_base;
@@ -1254,10 +1253,10 @@ static int __devinit omap_nand_probe(struct platform_device *pdev)
 			cfg.dst_addr_width = DMA_SLAVE_BUSWIDTH_4_BYTES;
 			cfg.src_maxburst = 16;
 			cfg.dst_maxburst = 16;
-			rc = dmaengine_slave_config(info->dma, &cfg);
-			if (rc) {
+			err = dmaengine_slave_config(info->dma, &cfg);
+			if (err) {
 				dev_err(&pdev->dev, "DMA engine slave config failed: %d\n",
-					rc);
+					err);
 				goto out_release_mem_region;
 			}
 			info->nand.read_buf   = omap_read_buf_dma_pref;