md: change the initialization value for a spare device spot to MD_DISK_ROLE_SPARE

The value for spare spot of sb->dev_roles is changed from
MD_DISK_ROLE_FAULTY to MD_DISK_ROLE_SPARE to keep align
with the value when the superblock is firstly created in
userspace.

Signed-off-by: Lidong Zhong <lzhong@suse.com>
Signed-off-by: Shaohua Li <shli@fb.com>

drivers/md/md.c

@@ -1857,7 +1857,7 @@ retry:
 		max_dev = le32_to_cpu(sb->max_dev);
 
 	for (i=0; i<max_dev;i++)
-		sb->dev_roles[i] = cpu_to_le16(MD_DISK_ROLE_FAULTY);
+		sb->dev_roles[i] = cpu_to_le16(MD_DISK_ROLE_SPARE);
 
 	if (test_bit(MD_HAS_JOURNAL, &mddev->flags))
 		sb->feature_map |= cpu_to_le32(MD_FEATURE_JOURNAL);