drm/i915: Use intel_fb_gtt_offset() also for gen2/3 primary plane

The code to determine the primary plane offset for gen2/3 looks
different than the code for gen4+, but in fact it's doing the same
thing. Let's make it uniform. Allows us to eliminate the 'obj' from
the list of local variables as well.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1478550057-24864-6-git-send-email-ville.syrjala@linux.intel.comReviewed-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/intel_display.c

@@ -3014,7 +3014,6 @@ static void i9xx_update_primary_plane(struct drm_plane *primary,
 	struct drm_i915_private *dev_priv = to_i915(dev);
 	struct intel_crtc *intel_crtc = to_intel_crtc(crtc_state->base.crtc);
 	struct drm_framebuffer *fb = plane_state->base.fb;
-	struct drm_i915_gem_object *obj = intel_fb_obj(fb);
 	int plane = intel_crtc->plane;
 	u32 linear_offset;
 	u32 dspcntr;
@@ -3109,8 +3108,11 @@ static void i9xx_update_primary_plane(struct drm_plane *primary,
 			   intel_crtc->dspaddr_offset);
 		I915_WRITE(DSPTILEOFF(plane), (y << 16) | x);
 		I915_WRITE(DSPLINOFF(plane), linear_offset);
-	} else
-		I915_WRITE(DSPADDR(plane), i915_gem_object_ggtt_offset(obj, NULL) + linear_offset);
+	} else {
+		I915_WRITE(DSPADDR(plane),
+			   intel_fb_gtt_offset(fb, rotation) +
+			   intel_crtc->dspaddr_offset);
+	}
 	POSTING_READ(reg);
 }