scsi: ufs-qcom: Do not return uninitialized err value

In func ufs_qcom_unvote_qos_all, err may be returned without being
initialized, so give it an initial value to avoid such case.

Change-Id: I56425601ae38d322a03af0916760ef2f166c2807
Signed-off-by: Can Guo <cang@codeaurora.org>