drm/i915/gen9: Increase PCODE request timeout to 50ms

After
commit 2c7d0602


Author: Imre Deak <imre.deak@intel.com>
Date:   Mon Dec 5 18:27:37 2016 +0200

    drm/i915/gen9: Fix PCODE polling during CDCLK change notification

there is still one report of the CDCLK-change request timing out on a
KBL machine, see the Reference link. On that machine the maximum time
the request took to succeed was 34ms, so increase the timeout to 50ms.

v2:
- Change timeout from 100 to 50 ms to maintain the current 50 ms limit
  for atomic waits in the driver. (Chris, Tvrtko)

Reference: https://bugs.freedesktop.org/show_bug.cgi?id=99345
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Acked-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/1487946730-17162-1-git-send-email-imre.deak@intel.com