net/mlx5e: Convert mlx5e_get_max_sq_wqebbs to u8

The return value of mlx5e_get_max_sq_wqebbs is clamped down to
MLX5_SEND_WQE_MAX_WQEBBS = 16, which fits into u8. This commit changes
the return type of this function to u8 for stricter type safety.
Signed-off-by: Maxim Mikityanskiy <maximmi@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Reviewed-by: Saeed Mahameed <saeedm@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/mellanox/mlx5/core/en.h

@@ -227,9 +227,11 @@ static inline int mlx5e_get_max_num_channels(struct mlx5_core_dev *mdev)
  * bytes units. Driver hardens the limitation to 1KB (16
  * WQEBBs), unless firmware capability is stricter.
  */
-static inline u16 mlx5e_get_max_sq_wqebbs(struct mlx5_core_dev *mdev)
+static inline u8 mlx5e_get_max_sq_wqebbs(struct mlx5_core_dev *mdev)
 {
-	return min_t(u16, MLX5_SEND_WQE_MAX_WQEBBS,
+	BUILD_BUG_ON(MLX5_SEND_WQE_MAX_WQEBBS > U8_MAX);
+
+	return (u8)min_t(u16, MLX5_SEND_WQE_MAX_WQEBBS,
 			 MLX5_CAP_GEN(mdev, max_wqe_sz_sq) / MLX5_SEND_WQE_BB);
 }