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 <[e-mail]>
Signed-off-by: Daniel Vetter <[e-mail]>
Link: http://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/omapdrm/Makefile

···
 obj-y += dss/
 obj-y += displays/
 
-ccflags-y := -Iinclude/drm
 omapdrm-y := omap_drv.o \
 	omap_irq.o \
 	omap_debugfs.o \