According to the spec (JESD220E chapter 7.2), while powering off/on the ufs
device, REF_CLK signal should be between VSS(Ground) and VCCQ/VCCQ2.

Link: https://lore.kernel.org/r/1610103385-45755-2-git-send-email-ziqichen@codeaurora.orgReviewed-by: Can Guo <cang@codeaurora.org>
Acked-by: Avri Altman <avri.altman@wdc.com>
Signed-off-by: Ziqi Chen <ziqichen@codeaurora.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>