fs/fat: Fix pathnames using '..' that lead to the root directory

If we end up back in the root directory via a '..' directory entry, set
itr->is_root accordingly. Failing to do that gives spews like
"Invalid FAT entry" and being unable to access directory entries located
past the first cluster of the root directory.

Fixes: 8eafae209c ("fat/fs: convert to directory iterators")
Reviewed-by: Tom Rini <trini@konsulko.com>
Signed-off-by: Tuomas Tynkkynen <tuomas.tynkkynen@iki.fi>

fs/fat/fat.c

@@ -710,13 +710,14 @@ static void fat_itr_child(fat_itr *itr, fat_itr *parent)
 	itr->fsdata = parent->fsdata;
 	if (clustnum > 0) {
 		itr->clust = clustnum;
+		itr->is_root = 0;
 	} else {
 		itr->clust = parent->fsdata->root_cluster;
+		itr->is_root = 1;
 	}
 	itr->dent = NULL;
 	itr->remaining = 0;
 	itr->last_cluster = 0;
-	itr->is_root = 0;
 }
 
 static void *next_cluster(fat_itr *itr)