net:stmmac: fix memleak in the open method

This patch is to fix a memory leak in the open method, it reviews error
conditions freeing the resources previously allocated and not freed in
cased of DMA failure.

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