mm/migrate: remove unneeded semicolons

Remove superfluous semicolons after function definitions.

Link: https://lkml.kernel.org/r/20210115110131.2359683-1-cy.fan@huawei.com
Signed-off-by: Chengyang Fan <cy.fan@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>