fs/reiserfs/stree.c: remove set but not used variables

fs/reiserfs/stree.c: remove set but not used variables

Fixes gcc '-Wunused-but-set-variable' warning:

fs/reiserfs/stree.c: In function search_by_key:
fs/reiserfs/stree.c:596:6: warning: variable right_neighbor_of_leaf_node set but not used [-Wunused-but-set-variable]

Link: http://lkml.kernel.org/r/1566379929-118398-3-git-send-email-zhengbin13@huawei.com
Signed-off-by: zhengbin <zhengbin13@huawei.com>
Reported-by: Hulk Robot <hulkci@huawei.com>
Cc: Jan Kara <jack@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>