media: mtk-vcodec: Remove duplicated include in mtk_vcodec_enc_drv.c

Fix following includecheck warning:
./drivers/media/platform/mtk-vcodec/mtk_vcodec_enc_drv.c:
linux/pm_runtime.h is included more than once.

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>