btrfs: merge calculations for simple striped profiles in btrfs_rmap_block

Use the same expression for stripe_nr for RAID0 (map->sub_stripes is 1)
and RAID10 (map->sub_stripes is 2), with equivalent results.
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/block-group.c

@@ -1816,11 +1816,10 @@ int btrfs_rmap_block(struct btrfs_fs_info *fs_info, u64 chunk_start,
 		stripe_nr = physical - map->stripes[i].physical;
 		stripe_nr = div64_u64_rem(stripe_nr, map->stripe_len, &offset);
 
-		if (map->type & BTRFS_BLOCK_GROUP_RAID10) {
+		if (map->type & (BTRFS_BLOCK_GROUP_RAID0 |
+				 BTRFS_BLOCK_GROUP_RAID10)) {
 			stripe_nr = stripe_nr * map->num_stripes + i;
 			stripe_nr = div_u64(stripe_nr, map->sub_stripes);
-		} else if (map->type & BTRFS_BLOCK_GROUP_RAID0) {
-			stripe_nr = stripe_nr * map->num_stripes + i;
 		}
 		/*
 		 * The remaining case would be for RAID56, multiply by