drm/i915/gvt: fix trace TRACE_INCLUDE_PATH

TRACE_INCLUDE_PATH should be a path relative to define_trace.h, not the
file including it. (See the comment in include/trace/define_trace.h.)

Cc: Zhi Wang <zhi.wang.linux@gmail.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Zhi Wang <zhi.a.wang@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/48b772795b7ab674f609ecad53b4882c66a8262a.1649852517.git.jani.nikula@intel.com
Reviewed-by: Zhi Wang <zhi.a.wang@intel.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>