net/mlx5e: Fix return value in case of module EEPROM read error

mlx5e_get_module_eeprom_by_page() has weird error handling.

First, it is treating -EINVAL as a special case, but it is unclear why.

Second, it tries to fail "gracefully" by returning the number of bytes
read even in case of an error. This results in wrongly returning
success (0 return value) if the error occurs before any bytes were
read.

Simplify the error handling by returning an error when such occurs. This
also aligns with the error handling we have in mlx5e_get_module_eeprom()
for the old API.

This fixes the following case where the query fails, but userspace
ethtool wrongly treats it as success and dumps an output:

  # ethtool -m eth2
  netlink warning: mlx5_core: Query module eeprom by page failed, read 0 bytes, err -5
  netlink warning: mlx5_core: Query module eeprom by page failed, read 0 bytes, err -5
  Offset		Values
  ------		------
  0x0000:		00 00 00 00 05 00 04 00 00 00 00 00 05 00 05 00
  0x0010:		00 00 00 00 05 00 06 00 50 00 00 00 67 65 20 66
  0x0020:		61 69 6c 65 64 2c 20 72 65 61 64 20 30 20 62 79
  0x0030:		74 65 73 2c 20 65 72 72 20 2d 35 00 14 00 03 00
  0x0040:		08 00 01 00 03 00 00 00 08 00 02 00 1a 00 00 00
  0x0050:		14 00 04 00 08 00 01 00 04 00 00 00 08 00 02 00
  0x0060:		0e 00 00 00 14 00 05 00 08 00 01 00 05 00 00 00
  0x0070:		08 00 02 00 1a 00 00 00 14 00 06 00 08 00 01 00

Fixes: e109d2b ("net/mlx5: Implement get_module_eeprom_by_page()")
Signed-off-by: Gal Pressman <gal@nvidia.com>
Reviewed-by: Alex Lazar <alazar@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/1762265736-1028868-1-git-send-email-tariqt@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: gal-pressman

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

@@ -2125,14 +2125,12 @@ static int mlx5e_get_module_eeprom_by_page(struct net_device *netdev,
 		if (!size_read)
 			return i;
 
-		if (size_read == -EINVAL)
-			return -EINVAL;
 		if (size_read < 0) {
 			NL_SET_ERR_MSG_FMT_MOD(
 				extack,
 				"Query module eeprom by page failed, read %u bytes, err %d",
 				i, size_read);
-			return i;
+			return size_read;
 		}
 
 		i += size_read;