net/mlx5e: Trim the length of the num_doorbell error

When trying to set num_doorbells to a value greater than the max number
of channels, the error message was going over the netlink limit of 80
chars, truncating the most important part of the message, the number of
channels.

Fix that by trimming the length a bit.

Fixes: 11bbcfb ("net/mlx5e: Use the 'num_doorbells' devlink param")
Signed-off-by: Cosmin Ratiu <cratiu@nvidia.com>
Reviewed-by: Dragos Tatulea <dtatulea@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Link: https://patch.msgid.link/1762681073-1084058-3-git-send-email-tariqt@nvidia.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Author: Cosmin Ratiu

drivers/net/ethernet/mellanox/mlx5/core/devlink.c

@@ -541,7 +541,7 @@ static int mlx5_devlink_num_doorbells_validate(struct devlink *devlink, u32 id,
 	max_num_channels = mlx5e_get_max_num_channels(mdev);
 	if (val32 > max_num_channels) {
 		NL_SET_ERR_MSG_FMT_MOD(extack,
-				       "Requested num_doorbells (%u) exceeds maximum number of channels (%u)",
+				       "Requested num_doorbells (%u) exceeds max number of channels (%u)",
 				       val32, max_num_channels);
 		return -EINVAL;
 	}