mtd, cfi, ubi: add missing writebufsize initialization

ff94bc40af3481d47546595ba73c136de6af6929 "mtd, ubi, ubifs: resync with Linux-3.14"
introduced the writebufsize field in struct mtd_info, which
is not initialized in the cfi_flash driver, which leads in
not working ubi on cfi flashes. Fix it

Signed-off-by: Heiko Schocher <hs@denx.de>
Reported-by: Andrew Ruder <andrew.ruder@elecsyscorp.com>
Acked-by: Stefan Roese <sr@denx.de>
Acked-by: Andrew Ruder <andrew.ruder@elecsyscorp.com>

drivers/mtd/cfi_mtd.c

@@ -226,6 +226,7 @@ int cfi_mtd_init(void)
 		mtd->flags		= MTD_CAP_NORFLASH;
 		mtd->size		= fi->size;
 		mtd->writesize		= 1;
+		mtd->writebufsize	= mtd->writesize;
 
 		mtd->_erase		= cfi_mtd_erase;
 		mtd->_read		= cfi_mtd_read;