Undoubtedly going to graves in order to seek help from dead is shirk (associating partner with Allah): قال الشامی: انہ ظن أن المیت یتصرف فی الأمور اعتقادہ ذلک کفر [الشامی: 3/427]
But, if the help is sought from Allah it may be allowed but having such a belief about mazar (that they are places where prayer is accepted, or traveling to it) is baseless. This kind of belief is not proved by the Quran and Hadith; therefore it should be avoided, especially in this age when the mazaraat have become hubs of sins and innovations and where men and women meet together and do many acts of shirk.
Allah (Subhana Wa Ta’ala) knows Best
Darul Uloom Deoband