bcachefs: Change "accounting overran journal reservation" to a warning

This doesn't need to be a BUG_ON(); the actual serious "things break"
condition is if the whole journal write overruns the available space,
and that has a fatal error, not a BUG_ON(). This check indicates we
screwed something up, but it should be a warning.

Signed-off-by: Kent Overstreet <[email protected]>

Author: Kent Overstreet

fs/bcachefs/journal_io.c

@@ -1848,7 +1848,8 @@ static int bch2_journal_write_prep(struct journal *j, struct journal_buf *w)
 
 	bch2_journal_super_entries_add_common(c, &end, seq);
 	u64s	= (u64 *) end - (u64 *) start;
-	BUG_ON(u64s > j->entry_u64s_reserved);
+
+	WARN_ON(u64s > j->entry_u64s_reserved);
 
 	le32_add_cpu(&jset->u64s, u64s);