[ARM] 5607/1: ep93xx: Use __iomem pointer on syscon write function

Change the reg argument of the ep93xx_syscon_swlocked_write function
to be an __iomem pointer. Fixes a number of build warnings.

Signed-off-by: Ryan Mallon <ryan@bluewatersys.com>
Acked-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>