drm/i915: Unalias obj->phys_handle and obj->userptr

We use obj->phys_handle to choose the pread/pwrite path, but as
obj->phys_handle is a union with obj->userptr, we then mistakenly use
the phys_handle path for userptr objects within pread/pwrite.

Testcase: igt/gem_userptr_blits/forbidden-operations
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=97519
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: stable@vger.kernel.org
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20161003124516.12388-2-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_drv.h

@@ -2281,21 +2281,19 @@ struct drm_i915_gem_object {
 	/** Record of address bit 17 of each page at last unbind. */
 	unsigned long *bit_17;
 
-	union {
-		/** for phy allocated objects */
-		struct drm_dma_handle *phys_handle;
-
-		struct i915_gem_userptr {
-			uintptr_t ptr;
-			unsigned read_only :1;
-			unsigned workers :4;
+	struct i915_gem_userptr {
+		uintptr_t ptr;
+		unsigned read_only :1;
+		unsigned workers :4;
 #define I915_GEM_USERPTR_MAX_WORKERS 15
 
-			struct i915_mm_struct *mm;
-			struct i915_mmu_object *mmu_object;
-			struct work_struct *work;
-		} userptr;
-	};
+		struct i915_mm_struct *mm;
+		struct i915_mmu_object *mmu_object;
+		struct work_struct *work;
+	} userptr;
+
+	/** for phys allocated objects */
+	struct drm_dma_handle *phys_handle;
 };
 
 static inline struct drm_i915_gem_object *