Because linux/err.h is unreferenced in smc_loopback.h file, so
remove it.
Signed-off-by: Zhengchao Shao <shaozhengchao@huawei.com> Reviewed-by: Simon Horman <horms@kernel.org> Reviewed-by: D. Wythe <alibuda@linux.alibaba.com> Signed-off-by: David S. Miller <davem@davemloft.net>