HwBufferMgr: fix SoftBufferAllocMgr (re)allocBuffers on FrameDim change
The patch fixes SoftBufferAllocMgr::allocBuffers
when FrameDim
changes. The bug will not be seen if the class is managed by a StdBufferCbMgr
(virtually all the current cases), but it will fail if the class SoftBufferAllocMgr
is used alone