CHROMIUM: drm/i915/intel_drv: reduce wait_for polling time

CHROMIUM: drm/i915/intel_drv: reduce wait_for polling time

Currently, 400kHz i2c transactions on i915 ddc adapters are gated by
long polling loops in the wait_for() macro.
For the case where the polling loops sleep, make them tighter by
converting a msleep(1) to usleep_range(50, 100);

A better solution might be to eliminate this polling entirely, and use
the i915 interrupts to detect state transitions instead of polling.

Signed-off-by: Daniel Kurtz <djkurtz@chromium.org>
BUG=chromium-os:26118
TEST=i2c reads over ddc succeed.  On a scope, single transactions no
  longer have large gaps.

Change-Id: I96cef50ed8a3d0ad8a3c6fa6f079234242fa17d3
Reviewed-on: https://gerrit.chromium.org/gerrit/17937
Reviewed-by: Daniel Kurtz <djkurtz@chromium.org>
Tested-by: Daniel Kurtz <djkurtz@chromium.org>
Commit-Ready: Daniel Kurtz <djkurtz@chromium.org>