[MTD] Initialize 'writesize'

Signed-off-by: Artem B. Bityutskiy <dedekind@infradead.org>
diff --git a/drivers/mtd/chips/map_rom.c b/drivers/mtd/chips/map_rom.c
index bc6ee9e..1b328b1 100644
--- a/drivers/mtd/chips/map_rom.c
+++ b/drivers/mtd/chips/map_rom.c
@@ -47,6 +47,7 @@
 	mtd->sync = maprom_nop;
 	mtd->flags = MTD_CAP_ROM;
 	mtd->erasesize = map->size;
+	mtd->writesize = 1;
 
 	__module_get(THIS_MODULE);
 	return mtd;