scsi: ufs: Ensure clocks are ON while running power change procedure

UFS driver is not holding clock requests while performing vendor-specific
power change settings. This can lead to un-clocked access if the
context which performs this power change sequence (Eg rls_handler) gets
scheduled out just before this vendor-specific steps and gets a chance
to run after clock gating delay. Clock gating can turn off the clock
during this time and can lead to un-clocked access.

CRs-fixed: 2549002
Change-Id: I49746ed5aa547271fc96cb33656f5fd9db42d07c
Signed-off-by: Veerabhadrarao Badiganti <vbadigan@codeaurora.org>