mm: remove the unused MIGRATE_PFN_ERROR flag

Now that we can rely errors in the normal control flow there is no
need for this flag, remove it.

Link: https://lore.kernel.org/r/20190814075928.23766-9-hch@lst.deSigned-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Ralph Campbell <rcampbell@nvidia.com>
Tested-by: Ralph Campbell <rcampbell@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

include/linux/migrate.h

@@ -167,7 +167,6 @@ static inline int migrate_misplaced_transhuge_page(struct mm_struct *mm,
 #define MIGRATE_PFN_LOCKED	(1UL << 2)
 #define MIGRATE_PFN_WRITE	(1UL << 3)
 #define MIGRATE_PFN_DEVICE	(1UL << 4)
-#define MIGRATE_PFN_ERROR	(1UL << 5)
 #define MIGRATE_PFN_SHIFT	6
 
 static inline struct page *migrate_pfn_to_page(unsigned long mpfn)