[media] mtk-vcodec: avoid warnings because of empty macros

Remove those gcc warnings:

	drivers/media/platform/mtk-vcodec/mtk_vcodec_dec_pm.c: In function 'mtk_vcodec_dec_pw_on':
	drivers/media/platform/mtk-vcodec/mtk_vcodec_dec_pm.c:114:51: warning: suggest braces around empty body in an 'if' statement [-Wempty-body]
	   mtk_v4l2_err("pm_runtime_get_sync fail %d", ret);
	                                                   ^

By adding braces.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>