net/mlx5e: Fix build break on 32bit

The cited commit caused the following build break in mlx5 due to a change
in size of MAX_SKB_FRAGS.

error: format '%lu' expects argument of type 'long unsigned int',
       but argument 7 has type 'unsigned int' [-Werror=format=]

Fix this by explicit casting.

Fixes: 3948b059 ("net: introduce a config option to tweak MAX_SKB_FRAGS")
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>
Link: https://lore.kernel.org/r/20230328200723.125122-1-saeed@kernel.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>