atheros: v3.18: change calls logic

atheros: v3.18: change calls logic

Check SoC family (AR5312+ or AR2315+) before call instead of checking it
inside the called function. Also convert ar{5312,2315}_init_device()
function to void, since they both return zero and nobody care about
return value.

Signed-off-by: Sergey Ryazanov <ryazanov.s.a@gmail.com>
SVN-Revision: 44713