net: mana: Don't overwrite port probe error with add_adev result

net: mana: Don't overwrite port probe error with add_adev result

In mana_probe(), if mana_probe_port() fails for any port, the error
is stored in 'err' and the loop breaks. However, the subsequent
unconditional 'err = add_adev(gd, "eth")' overwrites this error.
If add_adev() succeeds, mana_probe() returns success despite ports
being left in a partially initialized state (ac->ports[i] == NULL).

Only call add_adev() when there is no prior error, so the probe
correctly fails and triggers mana_remove() cleanup.

Fixes: a69839d4327d ("net: mana: Add support for auxiliary device")
Signed-off-by: Erni Sri Satya Vennela <ernis@linux.microsoft.com>
Link: https://patch.msgid.link/20260420124741.1056179-5-ernis@linux.microsoft.com
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>