ARM: dts: hix5hd2: don't change the existing compatible string

The SoC hix5hd2 compatible string has the suffix "-gmac" and
we should not change it.
We should only add the generic compatible string "hisi-gmac-v1".

Fixes: 0855950b

 ("ARM: dts: hix5hd2: add gmac generic compatible and clock names")
Signed-off-by: Dongpo Li <lidongpo@hisilicon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>