btrfs: btrfs_check_shared should manage its own transaction

btrfs: btrfs_check_shared should manage its own transaction

Commit afce772e87c3 ("btrfs: fix check_shared for fiemap ioctl") added
transaction semantics around calls to btrfs_check_shared() in order to
provide accurate accounting of delayed refs. The transaction management
should be done inside btrfs_check_shared(), so that callers do not need
to manage transactions individually.

Signed-off-by: Edmund Nadolski <[email protected]>
Signed-off-by: Jeff Mahoney <[email protected]>
Reviewed-by: David Sterba <[email protected]>
Signed-off-by: David Sterba <[email protected]>