fm10k: no need to continue in fm10k_down if __FM10K_DOWN already set

fm10k: no need to continue in fm10k_down if __FM10K_DOWN already set

Return early from fm10k_down() when we are already down, since that
means another thread is either already finished or has started going
down, so shouldn't conflict with them.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Krishneil Singh <Krishneil.k.singh@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Orabug: 25394529
(cherry picked from commit 1b00c6c064302354fce71d7c363945fe9e967f7c)
Signed-off-by: Jack Vogel <jack.vogel@oracle.com>