memory: correct the comment to DIRTY_MEMORY_MIGRATION

The dirty bit is DIRTY_MEMORY_MIGRATION. Correct the comment.

Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
Message-Id: <20190426020927.25470-1-richardw.yang@linux.intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
1 file changed