UBIFS: add a log overlap assertion

Add an assertion which checkes that the head of the log never overlaps with the
tail of the log.

Suggested-by: hujianyang <hujianyang@huawei.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>

fs/ubifs/misc.h

@@ -297,6 +297,7 @@ static inline int ubifs_next_log_lnum(const struct ubifs_info *c, int lnum)
 	if (lnum > c->log_last)
 		lnum = UBIFS_LOG_LNUM;
 
+	ubifs_assert(lnum != c->ltail_lnum);
 	return lnum;
 }