net: aquantia: return 'err' if set MPI_DEINIT state fails

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/net/ethernet/aquantia/atlantic/hw_atl/hw_atl_utils.c:260:7:
 warning: variable 'err' set but not used [-Wunused-but-set-variable]

'err' should be returned while set MPI_DEINIT state fails
in hw_atl_utils_soft_reset.

Fixes: cce96d18 ("net: aquantia: Regression on reset with 1.x firmware")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>