kgsl: Fix GPU freq being set to the max by default (320MHz)

Credit to SebastianFM: https://github.com/SebastianFM/SebastianFM-kernel/commit/831882790c5f09a4c9cf008322777f9aaa65d45b#diff-a20c5be16a95b59d8023e63f9ffa6523R987