btrfs: pass a pointer to get_range_bits() to cache first search result

btrfs: pass a pointer to get_range_bits() to cache first search result

Allow get_range_bits() to take an extent state pointer to pointer argument
so that we can cache the first extent state record in the target range, so
that a caller can use it for subsequent operations without doing a full
tree search. Currently the only user is try_release_extent_state(), which
then does a call to __clear_extent_bit() which can use such a cached state
record.

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>