reiserfs: balance_leaf refactor, format balance_leaf_paste_left

Break up balance_leaf_paste_left into:
balance_leaf_paste_left_shift
balance_leaf_paste_left_shift_dirent
balance_leaf_paste_left_whole

and keep balance_leaf_paste_left as a handler to select which is appropriate.

Also reformat to adhere to CodingStyle.
Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: Jan Kara <jack@suse.cz>