freedreno: small fix for flushing dependent batches

freedreno: small fix for flushing dependent batches

Flush a resource's previous write_batch synchronously.  Because a
resource's associated batches are not updated until after the flush
thread submits rendering to the kernel, this was causing a bit of
confusion in the following loop.  This fixes a bug that appeared with
recent stk.

Perhaps we need to re-work things a bit to clear out dependent patches
in the ctx's thread and use a fence to deal with the period between
when a flush is queued and when it is submitted to the kernel.  But
this will do until time permits a larger refactor.

Signed-off-by: Rob Clark <robdclark@gmail.com>