stmmac: prevent interrupt loop with MMC RX IPC Counter

If the DesignWare MAC is synthesised with MMC RX IPC Counter, an unmanaged
and unacknowledged interrupt is generated after some time of operation.

This patch masks the undesired interrupts.

Signed-off-by: Christian Ruppert <christian.ruppert@abilis.com>
Acked-by: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>