stmmac: fix sleep inside atomic

We cannot use spinlock when kmalloc is invoked with
GFP_KERNEL flag because it can sleep.
So this patch reviews the usage of spinlock within the
stmmac_resume function avoing this bug.

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