mtd: impa7: add missing __iomem annotation

Added missing __iomem annotation and used NULL instead of 0
in order to fix the following sparse warnings:

drivers/mtd/maps/impa7.c:82:32: warning: Using plain integer as NULL pointer
drivers/mtd/maps/impa7.c:96:34: warning: cast removes address space of expression
drivers/mtd/maps/impa7.c:96:34: warning: incorrect type in argument 1 (different address spaces)
drivers/mtd/maps/impa7.c:96:34: expected void volatile [noderef] <asn:2>*addr
drivers/mtd/maps/impa7.c:96:34: got void *<noident>
drivers/mtd/maps/impa7.c:108:34: warning: cast removes address space of expression
drivers/mtd/maps/impa7.c:108:34: warning: incorrect type in argument 1 (different address spaces)
drivers/mtd/maps/impa7.c:108:34: expected void volatile [noderef] <asn:2>*addr
drivers/mtd/maps/impa7.c:108:34: got void *<noident>
drivers/mtd/maps/impa7.c:109:45: warning: Using plain integer as NULL pointer

Signed-off-by: Jingoo Han <[e-mail]>
Signed-off-by: Brian Norris <[e-mail]>
Signed-off-by: David Woodhouse <[e-mail]>

drivers/mtd/maps/impa7.c

···
 		}
 		simple_map_init(&impa7_map[i]);
 
-		impa7_mtd[i] = 0;
+		impa7_mtd[i] = NULL;
 		type = rom_probe_types;
 		for(; !impa7_mtd[i] && *type; type++) {
 			impa7_mtd[i] = do_map_probe(*type, &impa7_map[i]);
···
 			mtd_device_parse_register(impa7_mtd[i], NULL, NULL,
 						  partitions,
 						  ARRAY_SIZE(partitions));
+		} else {
+			iounmap((void __iomem *)impa7_map[i].virt);
 		}
-		else
-			iounmap((void *)impa7_map[i].virt);
 	}
 	return devicesfound == 0 ? -ENXIO : 0;
 }
···
 		if (impa7_mtd[i]) {
 			mtd_device_unregister(impa7_mtd[i]);
 			map_destroy(impa7_mtd[i]);
-			iounmap((void *)impa7_map[i].virt);
-			impa7_map[i].virt = 0;
+			iounmap((void __iomem *)impa7_map[i].virt);
+			impa7_map[i].virt = NULL;
 		}
 	}
 }