stmmac: fix open funct when exit on error

This patch reviews the open function and fixes some
errors when exit with an error state.
It also moves the request_irq after core is initialized
when interrupts are properly masked.

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