drm/imagination: remove unnecessary header include path

drivers/gpu/drm/imagination/ includes local headers with the double-quote
form (#include "...").

Hence, the header search path addition is unneeded.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Matt Coster <matt.coster@imgtec.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250210102352.1517115-1-masahiroy@kernel.org
Signed-off-by: Matt Coster <matt.coster@imgtec.com>

Author: masahir0y

drivers/gpu/drm/imagination/Makefile

@@ -1,8 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0-only OR MIT
 # Copyright (c) 2023 Imagination Technologies Ltd.
 
-subdir-ccflags-y := -I$(src)
-
 powervr-y := \
 	pvr_ccb.o \
 	pvr_cccb.o \