net: stmmac: dwmac-intel-plat: remove config data on error

Remove the config data when rate setting fails.

Fixes: 9efc9b2b

 ("net: stmmac: Add dwmac-intel-plat for GBE driver")
Signed-off-by: Pan Bian <bianpan2016@163.com>
Link: https://lore.kernel.org/r/20210120110745.36412-1-bianpan2016@163.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>