stmmac: prevent dma init stuck in case of failures.

Add a limit when perform the DMA reset procedure
so, in case of problems (i.e. PHY reset failed) the
Kernel won't hang on the stmmac DMA initialisation
blocking the Kernels execution.

Signed-off-by: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>