mlxsw: core_linecards: Remove duplicated include in core_linecard_dev.c

Fix following includecheck warning:
./drivers/net/ethernet/mellanox/mlxsw/core_linecard_dev.c: linux/err.h is included more than once.

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Link: https://lore.kernel.org/r/20220727233801.23781-1-yang.lee@linux.alibaba.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>