net: phy: marvell: add sleep time after enabling the loopback bit

commit 18c532e4 upstream.

Sleep time is added to ensure the phy to be ready after loopback
bit was set. This to prevent the phy loopback test from failing.

Fixes: 020a45af ("net: phy: marvell: add Marvell specific PHY loopback")
Cc: <stable@vger.kernel.org> # 5.15.x
Signed-off-by: Muhammad Husaini Zulkifli <muhammad.husaini.zulkifli@intel.com>
Signed-off-by: Aminuddin Jamaluddin <aminuddin.jamaluddin@intel.com>
Link: https://lore.kernel.org/r/20221114065302.10625-1-aminuddin.jamaluddin@intel.com


Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>