scsi: ufshcd: suspend clock scaling before clocks are gated

Wait for pending clock scaling work to be done before clocks are
turned off in runtime suspend as scaling needs access to controller
registers.

Change-Id: I588544692fa6ceb75b8712b9116745f831586d68
Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>