drm/sis: remove unneeded -Iinclude/drm compiler flag

With the include directives under include/drm/ fixed, this flag is
no longer needed.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1493009447-31524-26-git-send-email-yamada.masahiro@socionext.com

drivers/gpu/drm/sis/Makefile

@@ -2,7 +2,6 @@
 # Makefile for the drm device driver.  This driver provides support for the
 # Direct Rendering Infrastructure (DRI) in XFree86 4.1.0 and higher.
 
-ccflags-y = -Iinclude/drm
 sis-y := sis_drv.o sis_mm.o
 
 obj-$(CONFIG_DRM_SIS)   += sis.o