Function ETH_DMAPrepare is broken

[Amomum]

DMA_CtrlDataInitTypeDef DMA_PriCtrlStr;

this structure is created but is not initialized, so call to DMA_Init triggers assert_failed.

Unfortunately I have no idea how to use ETH_DMAPrepare and when to call it. ETH_DMAFrameRx doesn't work in FIFO-mode (i.e. with DMA) if I just call it, so DMA should be prepared.. at some point.. i guess. But when and how exactly? I could not find any example for Ethernet with DMA.

[Eldar Khayrullin]

@Amomum Can you check the new commit e599218
PS I reset your previous commits (use original library files). If you need to fix them add a new pull request. Thank you