net: fman_memac: Don't use of_property_read_bool on non-boolean property managed

net: fman_memac: Don't use of_property_read_bool on non-boolean property managed

'managed' is a non-boolean property specified in ethernet-controller.yaml.
Since commit c141ecc3cecd7 ("of: Warn when of_property_read_bool() is
used on non-boolean properties") this raises a warning. Use the
replacement of_property_present() instead.

Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Reviewed-by: Sean Anderson <sean.anderson@linux.dev>
Link: https://patch.msgid.link/20250610114057.414791-1-alexander.stein@ew.tq-group.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>