drm/omap: 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/1493009447-31524-23-git-send-email-yamada.masahiro@socionext.com

drivers/gpu/drm/omapdrm/Makefile

@@ -6,7 +6,6 @@
 obj-y += dss/
 obj-y += displays/
 
-ccflags-y := -Iinclude/drm
 omapdrm-y := omap_drv.o \
 	omap_irq.o \
 	omap_debugfs.o \