After the completing the mpi_phy_start_resp, make phy enable completion as
NULL.

Link: https://lore.kernel.org/r/20191114100910.6153-3-deepak.ukey@microchip.comAcked-by: NJack Wang <jinpu.wang@cloud.ionos.com>
Signed-off-by: Npeter chang <dpf@google.com>
Signed-off-by: NDeepak Ukey <deepak.ukey@microchip.com>
Signed-off-by: NViswas G <Viswas.G@microchip.com>
Signed-off-by: NMartin K. Petersen <martin.petersen@oracle.com>