scsi: ufs: Fix race between shutdown and runtime resume flow

If UFS host device is in runtime-suspended state while UFS shutdown
callback is invoked, UFS device shall be resumed for register
accesses. Currently only UFS local runtime resume function will be invoked
to wake up the host.  This is not enough because if someone triggers
runtime resume from block layer, then race may happen between shutdown and
runtime resume flow, and finally lead to unlocked register access.

To fix this, in ufshcd_shutdown(), use pm_runtime_get_sync() instead of
resuming UFS device by ufshcd_runtime_resume() "internally" to let runtime
PM framework manage the whole resume flow.

Link: https://lore.kernel.org/r/20201119062916.12931-1-stanley.chu@mediatek.com
Fixes: 57d104c1

 ("ufs: add UFS power management support")
Reviewed-by: Can Guo <cang@codeaurora.org>
Signed-off-by: Stanley Chu <stanley.chu@mediatek.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>