net: stmmac: likely is useless in occasional function

The stmmac_adjust_link() function is called too rarely for having
likely() macros being useful.
Just remove likely annotation in it.

Signed-off-by: Corentin Labbe <clabbe.montjoie@gmail.com>
Acked-by: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Reviewed-by: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>