net: stmmac: Add Jose Abreu as co-maintainer

I'm offering to be a co-maintainer for stmmac driver.

As per discussion with Alexandre, I will arrange to get STM32 boards to
test patches in GMAC version 3.x and 4.1. I also have HW to test GMAC
version 5.

Looking forward to contribute to net-dev!

Signed-off-by: Jose Abreu <joabreu@synopsys.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Joao Pinto <jpinto@synopsys.com>
Cc: Alexandre Torgue <alexandre.torgue@st.com>
Cc: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Acked-by: Alexandre TORGUE <alexandre.torgue@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>