net/mlx5e: psp: Expose only a fully initialized priv->psp

net/mlx5e: psp: Expose only a fully initialized priv->psp

Currently, during PSP init, priv->psp is initialized to an incompletely
built psp struct. Additionally, on fs init failure priv->psp is reset to
NULL.

Change this so that only a fully initialized priv->psp is set, which
makes the code easier to reason about in failure scenarios.

Fixes: af2196f49480 ("net/mlx5e: Implement PSP operations .assoc_add and .assoc_del")
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/20260504181100.269334-3-tariqt@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>