drm/i915: Fix RPS pointer passed from wait_ioctl to i915_wait_request

In commit 2e1b8730 [v4.2]
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Mon Apr 27 13:41:22 2015 +0100

    drm/i915: Convert RPS tracking to a intel_rps_client struct

we converted the __i915_wait_request() to take a new intel_rps_client
struct (rather than having to pass fake drm_i915_file_private structs).
However, due to use of passing a void pointer, I didn't spot one
callsite in wait-ioctl was passing the wrong pointer.

Fwiw, the impact of this bug is zero. Along the rps path, we always
first call list_empty(rps) which when we pass in the wrong pointer
always evaluates to false and we return early and never chase the
invalid pointers.

The user visible impact is then wait-ioctl doesn't get the same
waitboosting as the other interfaces (set-domain, throttle), which is a
performance concern for the *very* few users of the wait interface.
There is also a libdrm_intel patch to use the wait-ioctl for
drm_intel_bo_wait_rendering() if anyone feels inclined to review
libdrm_intel patches.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
[danvet: Add Chris' explanation for why the impact of this is pretty
close to 0.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>