net: fman: memac: Uninitialized variable on error path

The "fixed_link" is only allocated sometimes but it's freed
unconditionally in the error handling.  Set it to NULL so we don't free
uninitialized data.

Fixes: 9ea4742a ("net: fman: Configure fixed link in memac_initialization")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Sean Anderson <sean.anderson@seco.com>
Link: https://lore.kernel.org/r/Ywd2X6gdKmTfYBxD@kili


Signed-off-by: Jakub Kicinski <kuba@kernel.org>