drm/i915: ignore pipe select bit when checking for LVDS register initialization

The Lenovo Thinkpad T410 has the LVDS_PIPEB_SELECT bit set in the LVDS
register when booted with the lid closed, even though the LVDS hasn't
really been initialized. Ignore this bit so that the VBT value will be
used instead.

Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>