mm/migrate_device: fix pgtable leak in migrate_vma_insert_huge_pmd_page

In the Linux kernel, the following vulnerability has been resolved: mm/migrate_device: fix pgtable leak in migrate_vma_insert_huge_pmd_page When migrate_vma_insert_huge_pmd_page() jumps to unlock_abort due to a PMD check failure, the pgtable allocated earlier via pte_alloc_one() is never freed, causing a memory leak. Added free_abort label to release the pgtable in error path.