libvpx

Declare function used by 'once' with 'void' parameters

Visual Studio is exceptionally picky about this:
vp9_reconintra.c(900): warning C4113: 'void (__cdecl *)()' differs in
parameter lists from 'void (__cdecl *)(void)'
[.build-x86_64-win64-vs10\vpx.vcxproj]

Change-Id: I564c7415f4608fd962be8c699d6133a996b545f7