disp: msm: sde: fix failure in perf mode clk update through debugfs

Setting perf tuning mode through debugfs during suspend can
result in underflow. Ensure that we are able to set rates,
or reset values and return to remain in normal mode.

Change-Id: Ib88de888690086d982b023b017083fee4e4d2091
Signed-off-by: Nilaan Gunabalachandran <ngunabal@codeaurora.org>