net/mlx5e: Fix printk format warning

Use "%zu" for size_t. Seen on ARM allmodconfig:

drivers/net/ethernet/mellanox/mlx5/core/wq.c: In function 'mlx5_wq_cyc_wqe_dump':
include/linux/kern_levels.h:5:18: warning: format '%ld' expects argument of type 'long int', but argument 5 has type 'size_t' {aka 'unsigned int'} [-Wformat=]

Fixes: 130c7b46 ("net/mlx5e: TX, Dump WQs wqe descriptors on CQE with error events")
Signed-off-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>