btrfs: clean up and optimize __check_raid_min_device()

btrfs: clean up and optimize __check_raid_min_device()

__check_raid_min_device() which was pealed from btrfs_rm_device()
maintianed its original code to show the block move. This patch cleans up
__check_raid_min_device().

Signed-off-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Orabug: 26287586

(Cherry picked from commit bd45ffbcb1f082e3c5a0bd56b1d7310d8b707ffb,
     drop the second argument of the btrfs_dev_replace_lock/unlock to
     match with the current kernel api)

Signed-off-by: Shan Hai <shan.hai@oracle.com>
Reviewed-by: Somasundaram Krishnasamy <somasundaram.krishnasamy@oracle.com>