mlxsw: core_env: Fix driver initialization with old firmware

The driver queries the Management Capabilities Mask (MCAM) register
during initialization to understand if it can read up to 128 bytes from
transceiver modules.

However, not all firmware versions support this register, leading to the
driver failing to load.

Fix by treating an error in the register query as an indication that the
feature is not supported.

Fixes: 1f4aea1f

 ("mlxsw: core_env: Read transceiver module EEPROM in 128 bytes chunks")
Reported-by: Tim 'mithro' Ansell <me@mith.ro>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://lore.kernel.org/r/0afa8b2e8bac178f5f88211344429176dcc72281.1713446092.git.petrm@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>