[media] s5p-mfc: remove volatile attribute from MFC register addresses

MFC register addresses are used only by writel/readl macros which already
takes care of proper register accessing.

Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Kamil Debski <k.debski@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>