net: enetc: remove the mm_lock from the ENETC v4 driver

net: enetc: remove the mm_lock from the ENETC v4 driver

Currently, the ENETC v4 driver has not added the MAC merge layer support
in the upstream, so the mm_lock is not initialized and used, so remove
the mm_lock from the driver.

Fixes: 99100d0d9922 ("net: enetc: add preliminary support for i.MX95 ENETC PF")
Cc: stable@vger.kernel.org
Signed-off-by: Wei Fang <wei.fang@nxp.com>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Link: https://patch.msgid.link/20250224111251.1061098-8-wei.fang@nxp.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>