ARM: 9240/1: dma-mapping: Pass (void *) to virt_to_page()

Pointers to virtual memory functions are (void *) but the
__dma_update_pte() function is passing an unsigned long.
Fix this up by explicit cast.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>