net: stmmac: platform: Delete a redundant condition branch

commit aed68640 upstream.

The statement of the last "if (xxx)" branch is the same as the "else"
branch. Delete it to simplify code.

No functional change.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Yongxin Liu <yongxin.liu@windriver.com>