exfat: fix uninit-value in __exfat_get_dentry_set

There is no check if stream size and start_clu are invalid.
If start_clu is EOF cluster and stream size is 4096, It will cause
uninit value access. because ei->hint_femp.eidx could be 128(if cluster
size is 4K) and wrong hint will allocate next cluster. and this cluster
will be same with the cluster that is allocated by
exfat_extend_valid_size(). The previous patch will check invalid start_clu,
but for clarity, Initialize hint_femp.eidx to zero.

Signed-off-by: Namjae Jeon <[email protected]>

namei.c

@@ -346,6 +346,7 @@ static int exfat_find_empty_entry(struct inode *inode,
 		if (ei->start_clu == EXFAT_EOF_CLUSTER) {
 			ei->start_clu = clu.dir;
 			p_dir->dir = clu.dir;
+			hint_femp.eidx = 0;
 		}
 
 		/* append to the FAT chain */