drm/i915: fix aliasing_ppgtt leak

drm/i915: fix aliasing_ppgtt leak

In i915_ggtt_cleanup_hw we need to remember to free aliasing_ppgtt. This
fixes the following kmemleak message:

unreferenced object 0xffff880213cca000 (size 8192):
  comm "modprobe", pid 1298, jiffies 4294745402 (age 703.930s)
  hex dump (first 32 bytes):
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
  backtrace:
    [<ffffffff817c808e>] kmemleak_alloc+0x4e/0xb0
    [<ffffffff8121f9c2>] kmem_cache_alloc_trace+0x142/0x1d0
    [<ffffffffa06d11ef>] i915_gem_init_ggtt+0x10f/0x210 [i915]
    [<ffffffffa06d71bb>] i915_gem_init+0x5b/0xd0 [i915]
    [<ffffffffa069749a>] i915_driver_load+0x97a/0x1460 [i915]
    [<ffffffffa06a26ef>] i915_pci_probe+0x4f/0x70 [i915]
    [<ffffffff81423015>] local_pci_probe+0x45/0xa0
    [<ffffffff81424463>] pci_device_probe+0x103/0x150
    [<ffffffff81515e6c>] driver_probe_device+0x22c/0x440
    [<ffffffff81516151>] __driver_attach+0xd1/0xf0
    [<ffffffff8151379c>] bus_for_each_dev+0x6c/0xc0
    [<ffffffff8151555e>] driver_attach+0x1e/0x20
    [<ffffffff81514fa3>] bus_add_driver+0x1c3/0x280
    [<ffffffff81516aa0>] driver_register+0x60/0xe0
    [<ffffffff8142297c>] __pci_register_driver+0x4c/0x50
    [<ffffffffa013605b>] 0xffffffffa013605b

Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Fixes: b18b6bde300e ("drm/i915/bdw: Free PPGTT struct")
Cc: stable@vger.kernel.org
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1470420280-21417-1-git-send-email-matthew.auld@intel.com