sna: Detect when SET_TILING fails to change tiling

If the swizzling is unknown, the SET_TILING ioctl silently converts the
request back to I915_TILING_NONE. In order to detect this, we need to
double check the ioctl parameters.

References: https://bugs.freedesktop.org/show_bug.cgi?id=90725#c21
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

src/sna/kgem.c

@@ -454,7 +454,7 @@ restart:
 	set_tiling.stride = stride;
 
 	if (ioctl(fd, DRM_IOCTL_I915_GEM_SET_TILING, &set_tiling) == 0)
-		return true;
+		return set_tiling.tiling_mode == tiling;
 
 	err = errno;
 	if (err == EINTR)