drm/i915: POSTING_READs are simply flushes and so irrelevant to tracing

As we use POSTING_READ to flush the write to the register before
proceeding, we do not care what the return value is and similar we do
not care for the read to be recorded whilst tracing register
read/writes.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
2 files changed