Assemble: keep MD_DISK_FAILFAST and MD_DISK_WRITEMOSTLY flag
Before updating superblock of slave disks, desired_state value
is set for the target state of the slave disks. But it forgets
to check MD_DISK_FAILFAST and MD_DISK_WRITEMOSTLY flags. Then
start_arrays() calls ADD_NEW_DISK ioctl-call and pass the state
without MD_DISK_FAILFAST and MD_DISK_WRITEMOSTLY.
Currenlty it does not generate any problem because kernel does not
care MD_DISK_FAILFAST or MD_DISK_WRITEMOSTLY flags.