msm: kgsl: Fix early exit condition in ringbuffer drain

The ringbuffer drain function can be called when the ringbuffer
start flag is not set. This happens on startup. Hence,
exiting the function early based on start flag is incorrect.
Simply execute this function regardless of the start flag.

Change-Id: Ibf2075847f8bb1a760bc1550309efb3c7aa1ca49
Signed-off-by: Shubhraprakash Das <sadas@codeaurora.org>