drm/amdkfd: Fix mmap write lock not release

In the Linux kernel, the following vulnerability has been resolved: drm/amdkfd: Fix mmap write lock not release If mmap write lock is taken while draining retry fault, mmap write lock is not released because svm_range_restore_pages calls mmap_read_unlock then returns. This causes deadlock and system hangs later because mmap read or write lock cannot be taken. Downgrade mmap write lock to read lock if draining retry fault fix this bug.