mtd: onenand: fix build warning for dma type

The samsung onenand driver passes around a dma address token
through a void pointer, which is incorrect and leads to
warnings like this one:

onenand/samsung.c:548:2: warning: passing argument 1 of '__fswab32' makes integer from pointer without a cast [enabled by default]
  writel(src, base + S5PC110_DMA_SRC_ADDR);
  ^

This patch makes it use dma_addr_t here, which is more appropriate.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Kyungmin Park <kyungmin.park@samsung.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: linux-mtd@lists.infradead.org
Signed-off-by: Brian Norris <computersforpeace@gmail.com>