scsi: ufs: Add checks before setting clk-gating states

Clock gating can be turned on/off selectively which means the associated
state information is only correct if the feature is enabled. This change
makes sure that we only look at state of clk-gating if it is enabled.

Link: https://lore.kernel.org/r/1596975355-39813-2-git-send-email-cang@codeaurora.org
Reviewed-by: Avri Altman <avri.altman@wdc.com>
Reviewed-by: Hongwu Su <hongwus@codeaurora.org>
Reviewed-by: Stanley Chu <stanley.chu@mediatek.com>
Reviewed-by: Bean Huo <beanhuo@micron.com>
Reviewed-by: Asutosh Das <asutoshd@codeaurora.org>
Signed-off-by: Can Guo <cang@codeaurora.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>