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.