md: keep recovery_cp in mdp_superblock_s

commit 907a99c ("md: rename recovery_cp to resync_offset") replaces
recovery_cp with resync_offset in mdp_superblock_s which is in md_p.h.
md_p.h is used in userspace too. So mdadm building fails because of this.
This patch revert this change.

Fixes: 907a99c ("md: rename recovery_cp to resync_offset")
Signed-off-by: Xiao Ni <xni@redhat.com>
Link: https://lore.kernel.org/linux-raid/20250815040028.18085-1-xni@redhat.com
Signed-off-by: Yu Kuai <yukuai3@huawei.com>

Author: XiaoNi87

drivers/md/md.c

@@ -1423,7 +1423,7 @@ static int super_90_validate(struct mddev *mddev, struct md_rdev *freshest, stru
 		else {
 			if (sb->events_hi == sb->cp_events_hi &&
 				sb->events_lo == sb->cp_events_lo) {
-				mddev->resync_offset = sb->resync_offset;
+				mddev->resync_offset = sb->recovery_cp;
 			} else
 				mddev->resync_offset = 0;
 		}
@@ -1551,13 +1551,13 @@ static void super_90_sync(struct mddev *mddev, struct md_rdev *rdev)
 	mddev->minor_version = sb->minor_version;
 	if (mddev->in_sync)
 	{
-		sb->resync_offset = mddev->resync_offset;
+		sb->recovery_cp = mddev->resync_offset;
 		sb->cp_events_hi = (mddev->events>>32);
 		sb->cp_events_lo = (u32)mddev->events;
 		if (mddev->resync_offset == MaxSector)
 			sb->state = (1<< MD_SB_CLEAN);
 	} else
-		sb->resync_offset = 0;
+		sb->recovery_cp = 0;
 
 	sb->layout = mddev->layout;
 	sb->chunk_size = mddev->chunk_sectors << 9;

include/uapi/linux/raid/md_p.h

@@ -173,7 +173,7 @@ typedef struct mdp_superblock_s {
 #else
 #error unspecified endianness
 #endif
-	__u32 resync_offset;	/* 11 resync checkpoint sector count	      */
+	__u32 recovery_cp;	/* 11 resync checkpoint sector count	      */
 	/* There are only valid for minor_version > 90 */
 	__u64 reshape_position;	/* 12,13 next address in array-space for reshape */
 	__u32 new_level;	/* 14 new level we are reshaping to	      */