ARM: imx: fix imx31-dt.c time-related warning

Commit 6bb27d73 "ARM: delete struct sys_timer" caused the following:

arch/arm/mach-imx/imx31-dt.c:56:2: warning: initialization from incompatible pointer type [enabled by default]
arch/arm/mach-imx/imx31-dt.c:56:2: warning: (near initialization for ‘__mach_desc_IMX31_DT.init_time’) [enabled by default]

This is because mx31_clocks_init_dt() returns int, whereas the .init_time
field prototype expects a function returning void. Implement a wrapper so
that the prototypes match.

Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Olof Johansson <olof@lixom.net>