mtd: mxc_nand: Fix warning on nr_parts unused variable

If CONFIG_MTD_PARTITIONS is not selected, then the following warning is generated:

CC drivers/mtd/nand/mxc_nand.o
drivers/mtd/nand/mxc_nand.c: In function 'mxcnd_probe':
drivers/mtd/nand/mxc_nand.c:1014: warning: unused variable 'nr_parts'

Fix it by marking nr_parts as __maybe_unused.

Signed-off-by: Fabio Estevam <[e-mail]>
Signed-off-by: Artem Bityutskiy <[e-mail]>
Signed-off-by: David Woodhouse <[e-mail]>

drivers/mtd/nand/mxc_nand.c

···
 	struct mxc_nand_platform_data *pdata = pdev->dev.platform_data;
 	struct mxc_nand_host *host;
 	struct resource *res;
-	int err = 0, nr_parts = 0;
+	int err = 0, __maybe_unused nr_parts = 0;
 	struct nand_ecclayout *oob_smallpage, *oob_largepage;
 
 	/* Allocate memory for MTD device structure and private data */