UPSTREAM: drm/i915/intel_i2c: reuse GMBUS2 value read in polling loop

UPSTREAM: drm/i915/intel_i2c: reuse GMBUS2 value read in polling loop

Save the GMBUS2 value read while polling for state changes, and then
reuse this value when determining for which reason the loops were exited.
This is a small optimization which saves a couple of bus accesses for
memory mapped IO registers.

To avoid "assigning in if clause" checkpatch errors", use a ret variable
to store the wait_for macro return value.

Signed-off-by: Daniel Kurtz <djkurtz@chromium.org>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
(cherry picked from commit 90e6b26d6b28ade684a4b16b856a74f27bc644bc)

Change-Id: I3ed6c8720e75f4e3a246128ba01b8cc9fc114f6b
Signed-off-by: Daniel Kurtz <djkurtz@chromium.org>