drm: Free the idr layers before calling idr_destroy()

drm: Free the idr layers before calling idr_destroy()

/* A typical clean-up sequence for objects stored in an idr tree, will
 * use idr_for_each() to free all objects, if necessary, then
 * idr_remove_all() to remove all ids, and idr_destroy() to free
 * up the cached idr_layers.
 */

We were missing the vital idr_rmove_all() step and so were leaking
the used layers for every dri client:

unreferenced object 0xf32133c0 (size 148):
  comm "plymouthd", pid 131, jiffies 4294678490 (age 2308.030s)
  hex dump (first 32 bytes):
    04 00 00 00 00 00 00 00 00 00 00 00 00 40 19 f3  .............@..
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
  backtrace:
    [<c04e5657>] create_object+0x124/0x1f1
    [<c07cf100>] kmemleak_alloc+0x4c/0x90
    [<c04db6a9>] kmem_cache_alloc+0xee/0x13c
    [<c05c3d25>] idr_pre_get+0x24/0x61
    [<f8315c9c>] drm_gem_handle_create+0x27/0x7f [drm]
    [<f89925b2>] i915_gem_create_ioctl+0x4f/0x71 [i915]
    [<f83148ac>] drm_ioctl+0x272/0x356 [drm]
    [<c04f27c4>] vfs_ioctl+0x33/0x91
    [<c04f31cf>] do_vfs_ioctl+0x46b/0x496
    [<c04f3240>] sys_ioctl+0x46/0x66
    [<c040325f>] sysenter_do_call+0x12/0x38
    [<ffffffff>] 0xffffffff

Fixes https://bugzilla.kernel.org/show_bug.cgi?id=15803

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Dave Airlie <airlied@redhat.com>