scsi: ufs: Fix imbalanced scsi_block_reqs_cnt caused by ufshcd_hold()

The scsi_block_reqs_cnt increased in ufshcd_hold() is supposed to be
decreased back in ufshcd_ungate_work() in a paired way. However, if
specific ufshcd_hold/release sequences are met, it is possible that
scsi_block_reqs_cnt is increased twice but only one ungate work is
queued. To make sure scsi_block_reqs_cnt is handled by ufshcd_hold() and
ufshcd_ungate_work() in a paired way, increase it only if queue_work()
returns true.

Change-Id: I35f870e49cc832bb6f4b58763e3240f05b98ec13
Signed-off-by: Can Guo <cang@codeaurora.org>
Signed-off-by: Ziqi Chen <ziqichen@codeaurora.org>