drm/i915: Use correct path to trace include

The header comment in include/trace/define_trace.h specifies that the
TRACE_INCLUDE_PATH needs to be relative to the define_trace.h header
rather than the trace file including it. Most instances get that wrong
and work around it by adding the $(src) directory to the include path.

While this works, it is preferable to refer to the correct path to the
trace file in the first place and avoid any workaround.
Signed-off-by: Thierry Reding <treding@nvidia.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20170901144954.19620-4-thierry.reding@gmail.com

drivers/gpu/drm/i915/Makefile

@@ -150,5 +150,3 @@ endif
 i915-y += intel_lpe_audio.o
 
 obj-$(CONFIG_DRM_I915) += i915.o
-
-CFLAGS_i915_trace_points.o := -I$(src)

drivers/gpu/drm/i915/i915_trace.h

@@ -1031,5 +1031,5 @@ TRACE_EVENT(switch_mm,
 
 /* This part must be outside protection */
 #undef TRACE_INCLUDE_PATH
-#define TRACE_INCLUDE_PATH .
+#define TRACE_INCLUDE_PATH ../../drivers/gpu/drm/i915
 #include <trace/define_trace.h>