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.comSigned-off-by: Paolo Abeni <pabeni@redhat.com>