[MTD] Initialize 'writesize'

Signed-off-by: Artem B. Bityutskiy <dedekind@infradead.org>
diff --git a/drivers/mtd/devices/phram.c b/drivers/mtd/devices/phram.c
index e09e416..6c7337f 100644
--- a/drivers/mtd/devices/phram.c
+++ b/drivers/mtd/devices/phram.c
@@ -151,6 +151,7 @@
 	new->mtd.owner = THIS_MODULE;
 	new->mtd.type = MTD_RAM;
 	new->mtd.erasesize = PAGE_SIZE;
+	new->mtd.writesize = 1;
 
 	ret = -EAGAIN;
 	if (add_mtd_device(&new->mtd)) {