btrfs: switch search_file_offset_in_bio to return bool

Function search_file_offset_in_bio() finds the file offset in the
file_offset_ret, and we use the return value to indicate if it is
successful, so use bool.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>